In a novel, you frequently have readers able to guess which character is the murderer, or equivalent in non-murder-mystery books merely by working out who has inadequate reasons to be on stage. Even if not, you know that it has to be somone on stage.
Quests and other forms of travel can limit this, but not too much. Meeting new people on the way means they are minor, unless you loop back to see them again. Even characters who appear only for the climax need to be introduce earlier, indirectly, even if not so heavily as Sauron in The Lord of the Rings. Or you get surprise at the price of wreaking the story structure.