try full-contact fighting and submission wrestling in prison for money for quite a few years.. fighting with broken bones and ignoring injuries (can't get a cast or stiches without getting put in the 'hole', so you learn how to sew your own cuts shut with sharpened guitar string and thin 'beading line').. no real 'rules', and where the solution to every problem is murder.. literally.. for some guys. so long as your willing to go further and harder than the other guy, you won't get fucked with.. but then you end up getting jumped by Indians and kneegrows and you gotta learn to "do your worst, fast and first".
takes some effort to lose that mentality when you get out though.