In the movie Interstellar, why does Cooper send the “STAY” message? When Cooper winds up in the tesseract (event Z), there are two related events that are in his past that he knows about: the reception of the coordinates of the NASA base (event A) and the goodbye scene in which Murph tells him that the “ghost” told her “STAY” (event B) which he ignores. There’s also the related event of Murph’s reception of data on Gargantua through the wristwatch (event C), but unlike the other two this is, I think, not a past event that Cooper knows about before actually causing it.

I get that cause and effect are time inverted here, in that event Z allows Cooper to cause events A, B and C, and that there’s a loop in that event Z leads to A and A leads to Z, with another loop in that B needs to be ineffective in order to allow Z to happen which in turn leads to B. I think I understand the A-C-Z events, it seems that Cooper realizes that by ensuring the A-Z loop he can also cause C which he hopes allows Murph to solve the gravity problem (which she does).

I have trouble understanding the B-Z events though. Before his realization, Cooper seems to at first want to prevent himself from leaving on the space journey, which is why he uses the books to spell out “STAY” (event B). But why spell out a message that he already knows he will / has ignore(d)? Should I assume he has simply forgotten about the message? Or that he is so overcome with emotion he’s acting irrationally? Is there another explanation or something I missed? I realize there’s a potential paradox if Cooper would not cause B, or would cause an alternate B with a less ambiguous message like “COOPER STAY WITH YOUR DAUGHTER AND GET THE FOLLOWING DATA TO DR BRAND”, but that still doesn’t quite help me understand it.

EDIT: there's a related question on “Why Cooper didn't simply not give the co-ordinates of NASA?”, but the answer given there does not (to me) really resolve the contradiction of Cooper sending a message he (as I understand it) already knows is ineffective.

In the movie Interstellar, why does Cooper send the “STAY” message? When Cooper winds up in the tesseract (event Z), there are two related events that are in his past that he knows about: the reception of the coordinates of the NASA base (event A) and the goodbye scene in which Murph tells him that the “ghost” told her “STAY” (event B) which he ignores. There’s also the related event of Murph’s reception of data on Gargantua through the wristwatch (event C), but unlike the other two this is, I think, not a past event that Cooper knows about before actually causing it.

I get that cause and effect are time inverted here, in that event Z allows Cooper to cause events A, B and C, and that there’s a loop in that event Z leads to A and A leads to Z, with another loop in that B needs to be ineffective in order to allow Z to happen which in turn leads to B. I think I understand the A-C-Z events, it seems that Cooper realizes that by ensuring the A-Z loop he can also cause C which he hopes allows Murph to solve the gravity problem (which she does).

I have trouble understanding the B-Z events though. Before his realization, Cooper seems to at first want to prevent himself from leaving on the space journey, which is why he uses the books to spell out “STAY” (event B). But why spell out a message that he already knows he will / has ignore(d)? Should I assume he has simply forgotten about the message? Or that he is so overcome with emotion he’s acting irrationally? Is there another explanation or something I missed? I realize there’s a potential paradox if Cooper would not cause B, or would cause an alternate B with a less ambiguous message like “COOPER STAY WITH YOUR DAUGHTER AND GET THE FOLLOWING DATA TO DR BRAND”, but that still doesn’t quite help me understand it.

EDIT: there's a related question on “Why Cooper didn't simply not give the co-ordinates of NASA?”, but the answer given there does not (to me) really resolve the contradiction of Cooper sending a message he (as I understand it) already knows is ineffective.