During Breaking Bad season 4, Don Eladio intended to keep Jesse in Mexico as a permanent employee. Gus and Mike pretended to accept that arrangement, but they had a secret plan of their own, which they kept secret even from Jesse. The only explanation he got was a vague reassurance from Mike, some time after Don Eladio revealed his intentions, that "either we're all going home, or none of us are."
From the writer's point of view, of course it was a great use of suspense, to keep the plan from the audience until Gus excused himself from the party. But is there any plausible in-story reason why Gus decided it was better for him to keep Jesse in the dark?
The risks are obvious - Jesse's reaction to the news that he is not going home could have been violent enough to upset the celebratory mood. Without the celebration, Gus's plan wouldn't have worked. It was lucky for Gus that Jesse remained calm long enough to talk to Mike in private.
It's possible that Don Eladio had ordered Gus not to tell Jesse what was going to happen, but Gus could have told him anyway and Jesse would be able to act surprised without actually being at risk of doing something counter-productive in a panic.
The other possibility, that Gus didn't know Don Eladio's intentions either, doesn't seem likely to me. They must have had some kind of agreement before Gus went to Mexico, and if Don Eladio altered the deal, then Gus should have shown a little anger or disappointment. Even if, as Don Eladio thought, Gus was in a bad negotiating position, the acceptance of yet another unreasonable demand shouldn't have come so easy.
So I conclude that Gus had accepted that demand as part of the original agreement, and chose to allow Don Eladio to shock Jesse with the news that he "belongs to the cartel now". Why?