system
Given the following post, respond as if you're commenting on Reddit:
human
[Fight Club][Spoiler] Why did other people start joining when they saw him fighting?

I mean if i saw someone fighting himself i would avoid him.
gpt
Frustration. In their jobs they have no power and no real outlet for the rage and anger caused by whatever asshole was put in charge of them. Here they see a man who clearly enjoys getting hurt and they want to hurt someone. Once they've started it reawakens something primal, showing them that this is supposed to be the natural order to things. 

You're mistaken on how you'd act. You wouldn't avoid him, you'd watch him. You'd consider it entertainment for a while, as did the men watching him, and then you'd either lose interest after a while or you'd initiate if someone else didn't do it for you. And that's when the cracks start to form. Before you know it, you're talking about things you're not supposed to and bringing your friends and co-workers into this activity started by some crazy guy kicking the shit out of himself.