It occasionally happens thatt a lunar landing goes fine but does suffer a non-critical failure (fixed by the crew, or whatever). All your people return safely (as per Kennedy's stated goal), but the game doesn't give you credit for the landing--it even docks you 10 points' prestige! Any other mission might have cost you prestige, but would stil have given you credit for accomplishing its objective(s): docking, duration, etc., so long as those part(s) of the mission did succeed. But on the lunar landing, if it doesn't all go smoothly, victory is snatched from your fingers, as it were.