What is the base rate fallacy?

Judging by the story in front of you and forgetting how often the thing actually happens.

"This sequel has amazing buzz, it'll open at #1 for weeks", maybe. But how often does any film hold #1 for weeks? That background frequency is the base rate, and it should be your starting number before the story adjusts it up or down.

Markets priced on vibes instead of base rates leave a gap, and that gap is what sharp bettors eat. The single best opening question in forecasting is the least exciting one: how often does this usually happen?