system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do non-fighters collapse when they get elbowed in the head, but MMA fighters can take it with the punches so to speak?

Watching a UFC fight, you see fighters elbow as hard as possible against their opponents face. The fight goes on. Whereas when Metta World Peace elbowed James Harden, he was on the floor clutching his head and the game was stopped. Both muscular men throwing elbows. If anything the MMA elbow should be more effective in being a trained move.
gpt
Med student and martial arts buff here.

Most people just aren't used to getting hit.  It's a huge deal for most people because it's an egregious violation of all kinds of social norms, it destroys their pre-concieved notions about themselves and other people, and they just aren't accustomed to pain in any form.

It doesn't take a lot of training to "beat" this reaction out of people.  You can learn pretty quickly that getting hit in the head or face isn't necessarily the end of the world.  It's never fun, but you can easily learn to deal with it, up to a point.

Only up to a point, however.  When you get hit hard enough, it can start to cause real problems, but the phenomenon you describe in the thread title is as much psychological as anything else.