Success in Hollywood is never guaranteed. Actors can spend months working twelve-hour days on a set only for a movie to debut well below expectations both critically and financially. I can only imagine the dread of putting in time on a movie that has all the signs of being a flop, though it's worth noting that sometimes the actors get it wrong.
A Reddit thread had tons of people chiming in with examples when this happened, starting with a pretty notable example. SpaceTimer81 brought up one of the best Julia Roberts movies, and how two stars thought it was going to be a bomb:
