In "Beyond the Wall" (Game of Thrones, S07E06), the Night King throws a spear towards one of the three dragons, which is seen somewhere very far. Meanwhile, Daenerys, along with her other dragon, probably Drogon, is seen somewhat nearer to him and engaged in a mission to save Jon Snow on the ground.
It seems that the Night King can easily have attacked that dragon. Why did he choose the furthest flying dragon?
You've pointed at a good flaw. Drogon would have been an equally valid target.
But there are some options here as to why the NK chose Viserion over Drogon.
Although the ice spear did penetrate Viserion's skin with relative ease, Drogon is a considerably larger and stronger dragon.
We don't know much about the ice spear and whether it has any magical qualities that help with killing dragons. But given that Qyburn's ballista would make for an effective weapon too, I'm going to assume that dragon scales can be penetrated by brute force alone, without any magic. The ice spear was thrown with a tremendous amount of force.
But maybe killing Drogon was a stretch. He's a bigger dragon, and looks to be more armored as well. Maybe the Night King wasn't sure that it'd kill Drogon, and therefore he focused on the smaller, weaker dragons first.
Viserion was hit, couldn't fly anymore, and hit the ice with a considerable impact. When Dany flies away later, you can see that the mark Viserion left on the ice is by far the largest, thus showing that Viserion made a high velocity, high impact landing.
Drogon was on the ground. Even if he were to be hit in the same fashion as Viserion, he wouldn't hit the ground with such an impact, thus not knocking him out or killing him on impact. This may give Drogon (or Danaerys) the time to deal with the spear.
Viserion did lose a lot of blood very quickly; but Drogon is comparatively larger and more armored, would bleed less, and is maybe able to shrug it off more easily (similar to why stabbing a dog-sized animal with a dagger will kill it, but stabbing an elephant-sized animal will only wound it)
There is another thing to consider here. The spear hit Viserion under the wing. I'm not sure how much of a marksman the Night King is, but he hit Viserion in a place that would prevent him from flying, which is exactly how he should have taken Viserion down. It's also likely that the dragons are less armored near their wings, because armoring would chafe them during flying. They need a fair range of movement with their wings.
This is pure speculation, but if we assume that the Night King was aiming for a weak spot near the base of the wing, Drogon would not be a viable target as he was using his wings to rest on the ground, and therefore covering it. The weak spot would not be visible/hittable by the Night King.
Even if he could pierce Drogon's wing to hit the weak spot anyway, he had no line of sight to the weak spot and would be guesstimating his throw. Since this theory assumes that the Night King was aiming precisely, that makes Drogon a difficult target to accurately hit (exactly on the weak spot).
Comparatively, the flying dragons were better targets, as their weak spots are more exposed to those below them.
Looking at the linked image in GhotiandChips' answer, from the Night King's perspective, most of what he could hit on Drogon seems to either be pretty well armored, or invisible due to the wing covering line of sight to it.
It should have been clear to the Night King that Drogon was the transport dragon, carrying Dany and soon also the others. This slows Drogon down. He is also not able to just up and leave, because he can't leave Dany or the others, who will be quickly overwhelmed by the wights.
The Night King wasn't trying to kill one dragon, he was trying to kill multiple dragons. He obviously did not stop at killing one. Though we didn't see him throw a third spear, nor target Rhaegal specifically, it seems fair to assume that he was trying to kill all the dragons.
If he kills Drogon first, Rhaegal and Viserion can immediately fly away. They are already in the air, mobile, and they don't have to take people along with them.
If he kills a flying dragon first, Drogon can't just fly away. Not only will it take him more time to leave (due to not flying already), he also needs to load people, and presumably fly more safely so that the people do not fall off (evidenced by Jorah almost falling off when Drogon dodged the spear).
If you're trying to kill as much as you can, start by killing those who can run away to safety quickly, and kill the slow ones later.
Just my own believes, but what always explains every White Walker decision question to me:
I really believe all along that the Night King is always just provoking them. I feel that he is not in a rush because he believes he already won the war. Many times it just seems like he is always taunting everyone. He is always showing off. It always feels like if only the White Walkers moved, they could end everything.
In Season 7 Episode 6 the White Walkers could have ended everything so many times. They let Jon's crew stay in that little island what seemed to be days until the ground freeze and the Wights decide to attack. They could have thrown javelins, and I suspect that they could even use their powers to freeze the ground faster.
He could have taken any dragon, IMO, but he decided to just show off getting another one just to panic them. I don't feel he is in a rush to kill any of them. I don't believe they feel the necessity to kill everyone just because they can. I feel they WANT THIS WAR, but they want to appreciate it. This is the kind of personality I feel from them: they like to spread fear. Remembering that they once passed through Sam and left him there. It seemed more enjoyable to see him scared to death.
Also, a major show off moment, IMO, was when the Night King saw Jon leaving in the boat in Season 5 Episode 8, and raised his hands to summon every dead in the fight.
Since we're covering all the possibilities, there's one more that would tie up a lot of the in-universe questions (such as, why did the army of dead react so slowly?) and out-of-universe questions (such as, why not just CGI it differently so Viserion was closer?!?).
If he could hit a moving dragon at that distance with an ice spear, he could hit some sleeping humans.
The army of wights ignored the frozen ice until Sandor accidentally noticed it had re-frozen. Not responding to that would have been suspicious - even then, they were slow to react, slow to charge and didn't attack from all sides (climbing the back of the rock) until moments before the dragons arrived.
The white walkers themselves just hung at the back and watched until the dragons arrived. We've seen they can freeze water with their presence - they didn't. They could probably have reanimated Thoros while the others slept, (before anyone even noticed he had died), and have him kill one or more in their sleep - they didn't. They could have provided ice spear artillery during the fight - they didn't. And he was in no hurry at all to take that second shot that was aimed at Drogon.
At best, he seems casually unconcerned about these particular humans.
We know from the Night King's encounter with Bran that he has some sort of as-yet unknown abilities to see or understand things across time and space. And let's face it, Jon has been very useful so far and may continue to be:
And while (thanks largely to Sam) he did pay a part in beginning dragonglass mining, he again lost most of it on this expedition.
I'm not saying the Night King might have been conspiring for a long time to keep Jon alive, he's not that useful and brings some risks too, just that he might at this moment:
As shown in these images, Drogon poses as much (if not more) of a threat as the other dragons from the moment he lands, breathing fire continually.
Drogon is even seen burning away his army of the dead as he's walking up the hill to choose a target for his spear.
The intelligent (and even intuitive) choice would have been Drogon:
Whether the Night King operates with conscious intelligence, or whether he operates with animalistic, predatory intuition, Drogon would have been the obvious choice.
The true answer is that the Night King isn't being driven by personal, realistic logic but by plot-logic. In other words, he was written to choose Viserion because choosing Drogon, who's carrying Daenerys (and company), would result in a peril that they didn't want to write (a direction they didn't want the plot to take). Daenerys has plot armor, so if Drogon at that moment is carrying her, Drogon will survive (until Daenerys' plot armor expires, of course).
Just accept that this is a weakly written moment in the show where logic wasn't prioritised (which contrasts strongly with the source material written by GRRM, and is why it stands out to you as confusingly illogical).
Possible in-universe, logical explanations I'm going on a limb and being very generous to the show by accepting any of the following as the actual logic they intended to write here:
Because Viserion was attacking his army at that moment and Drogon was not. Night king need his soldier for the coming war and maybe he was overconfident that he can attack Drogon easily later as he is too near for a possible attack. But later we see that he miss Drogon.
Drogon and Viserion are simultaneously breathing fire on the Army of the Dead
Commented
Aug 21, 2017 at 8:50
Winging a dragon in flight is more likely to kill it from the impact after it falls to the ground, as opposed to stabbing a nearby creature that may turn on you and breathe fire in your face or eat you.
There were plenty of logic holes in "Beyond the Wall," but this one is one of the easier ones to speculatively fill. I say speculatively because at this point in the progression of the divergent-from-the-books plot of the series, we as viewers have very little information on the motivations, thought processes, and history of the Night King, making it extremely difficult to explain why he makes the decisions that he does and what his end game is (adding narrative suspense).
Making a guess as to the Night King's dragon-targeting heuristic -> at the moment in the episode when he picks up an ice spear, he's facing three active threats in the forms of Dany's dragons as well as the more peripheral threat of Jon Snow, who has demonstrated his ability to kill white walkers with Longclaw, his Valyrian steel sword. From a purely tactical standpoint, the two dragons in the air (Viserion & Rhaegal) are the biggest threats due to the fact that they are airborne and mobile. Drogon at this point in time is currently grounded and is unlikely to take off until commanded to by Dany, who is occupied with assisting Jon's companions onto the back of the dragon. We can reasonably assume that Drogon's dragonfire is limited in range and that the Night King is out of that range. Drogon is definitely among the top 3 threats at this moment, however, targeting him first would only make sense if the Night King did not feel that the dragons or Jon Snow posed any significant threat, making Drogon the most valuable dragon to turn while simultaneously trapping Dany, Jon, and their party.
Given the relative impossibility of neutralizing both Drogon and Jon with one spear, targeting Drogon would result in the Night King attracting aggro/focus from Jon Snow as well as Viserion & Rhaegal simultaneously. The Night King could possibly take out one more dragon hurtling towards him with dragon fire with his second spear but his chances of survival would be much lower than picking off Viserion first. The Night King actually does target Drogon next who Dany is forced to take airborne immediately, leaving Jon behind to certain (were it not for plot armor) death - the second ice spear very narrowly misses as well.
I think the night king wants a bigger army. It would be logical to taunt as many of the southern kings as possible into attacking him... on his own land, where the white walkers are strongest and the mortal armies have to fight hunger and the cold.
Now, by attacking and killing Dany und Jon he could hurt his enemies, but they are the only ones foolish enough to confront him openly. If they die, than nobody will invade the north, and the white walkers will eventually have to head into the sunny south, something they probably want to do as late as possible. And to be honest, killing two kings will just make other men take over, without the realm being much weaker.
It appeared to me that Visarion was flying in to attack the White Walkers & the Night King - had the Night King have thrown the spear at any other dragon, they would have been burned before he could have thrown another spear.
The Night King was removing the greatest threat to himself at that moment in time.
Narrative structure.
Dragon is supposedly much larger than his siblings, large enough to fly multiple people between Eastwatch and the ambush, which can’t be that big a distance considering Gendry ran back there.
Kill him and the Mother of Dragons and Azor Ahai are stranded in that glacier and they are both eventually overwhelmed and killed. That is why the Night’s King chose to attack the smaller moving target rather than the stationary larger target.
Ice dragons are a separate species that is rumored to exist in the lore of the books. The show didn’t bother to lay the narrative groundwork in earlier seasons about if there could be ice-breathing dragons just as there are fire-breathing dragons.
And even if they had, they want the narrative and visual spectacle of Azor Ahai and the Mother of Dragons fighting the Night’s King with all three mounted on dragons of their own. For this to have the maximum dramatic impact, they want viewers to be invested in who the mount of the Night’s King is, not a random new species of the dragon being introduced at the eleventh hour. They can’t kill Dragon, since doing that removes Daenerys from the fight, and they can’t kill Rhaegal, because he will bond with Jon. So, Viserion quite literally picked the short straw. And instead of a living ice-breathing dragon, we are going to get an undead dragon who may or may not breathe ice.
To preserve some degree of narrative integrity, the writers had the leader of the Others try to kill Dragon right at the end, but this dragon manages to dodge, whereas Viserion was caught cold.
Tyrion is not going to be happy about this.
Simply put, Drogon is more maneuverable on land than Viserion is in the air. And the less maneuverable target is the easier one to land a (devastating) blow on.
You can watch Drogon in the fight and see that he has substantial lateral movements even as he stays mostly in the same place. This makes it easy for an attack to miss entirely, or otherwise fail to do adequate damage. The swarming wights also act as a bit of a shield: if one clambers up Drogon at an inconvenient moment then the ice spear may hit it, reducing the effectiveness of the attack.
Viserion, on the other hand, has an extremely predictable path: he's going to fly forward in pretty much the exact same direction for several seconds, as he has a ton of momentum and not a lot of ability to rapidly change direction mid-air. While the Dragons have demonstrated a limited capacity to hover, which is a pretty impressive flight maneuver, they've never been shown as having exceptional mobility. Furthermore, neither Viserion nor anyone else is even aware of the Night King's impending attack, or even considering the possibility that a meaningful ground-to-air strike can be made, so the airborne dragons are acting as if they're unassailable.
All-in-all, Viserion is the easier target: he can't move that much, nor is he even in a mindset to consider taking evasive actions.
My guess, throwing a spear gave the night king the chance to miss the shoot and try again without being noticed. Throwing the spear against Drogon would be absolutely noticeable, with all the dragons in the air in a matter of seconds.
This certainly can be deemed as not-accounting-for-logic writing and an attempt to keep intact, the central characters now, to the story. Drogon was carrying Danny and was going to probably take Jon. If the night king indeed went for Drogon first, which in all fairness he could have, the show would basically come to a stand still.
There could be several assumptions at this point as to why the NK went for viserion but it all comes down to making the episode little more action packed. Viserion was flying, NK is a master marksman and can throw the ice spear so perfectly that he can bring down a fire breathing dragon with one blow AND turn it into his own. Poor writing went oblivious to the fact that Drogon, the more powerful and stronger, was just a sitting duck, who was not targeted by the NK. I suppose we will have to wait to find out if indeed there is an inner meaning to this. Or this would just be a lose moment in an erstwhile brilliant series.
