Sometimes, unfortunately, people need to get smacked around, or even have the shit beat out of them, because absolutely nothing else will get through to them.
In the case of someone like Chris, he lacks the executive functions to control his impulses on a rational level. There is no delay of gratification for a better outcome, and no anticipation of future consequences that can override his impulsivity for immediate reward. All humans are like this to some degree, but Chris is an extreme example.
Physical pain bypasses all of this and works on a more fundamental level. You don't avoid pain on a conscious level, it's operates on a more primitive learned behavior that even rather simple animals are capable of. It works because it's part of the same circuitry as the simple reward mechanism that drives people like Chris. This is also why you can train snails.
EDIT: There are drugs that can inhibit the reward mechanism to control impulsivity, but they have the side effect of making you rather miserable.