It can be perfectly rational to ignore your own judgment and just copy the crowd
Economists Sushil Bikhchandani, David Hirshleifer and Ivo Welch showed in 1992 that once enough people in sequence make the same visible choice — which restaurant to enter, which stock to buy — it becomes rational for everyone who follows to copy them and ignore their own private information, since the crowd seems to carry more evidence than one person's judgment. The catch: the cascade can rest on the thin original guesses of just the first few people, with no new information added since.