Jay Dobyns during his career with the ATF conducted over 500 undercover operations. During that time Jay did it all, was shot in the chest at point-blank range, got into fights...all of the things we've seen in the movies. 

Jay worked hard to not let the experience change him, but it's not possible. Not only does he have to keep himself harden himself to do this dangerous work...but also to keep himself alive as he is slowly removed from reality. 

Pete A Turner dives in like only an operator can.