Why do crowds sometimes act differently than individuals?

Have you ever been in a crowded concert or sports stadium, and suddenly everyone around you is doing something you'd never do alone? Maybe screaming louder than you thought possible, or rushing toward the stage when the music starts? One person is cautious. A hundred people together can turn into a wave. What changes when we join a crowd?
Here's the strange part: when you're in a big group, your brain shifts gears. It stops thinking "what should I do?" and starts thinking "what is everyone else doing?" It's like your decision-making switches from solo mode to follow-the-group mode. Psychologists call this "deindividuation" — you feel less like a single person and more like part of one big organism.
