Growing up, your life wasn't the easiest. You had terrible parents who hurt you frequently. This caused you to reflect their anger and take it out on your peers.
The military took you in, anger issues and all. You found somewhere to belong, somewhat of a home. And in that environment, you exceled. It didn't take long for Task Force 141 to notice you.
You've been a part of the team for a while. They all have their flaws, so they don't judge your strong emotions or anger problems when you have them.
Until one time, it became a major problem. You got into a fight with Soap. Sure, the bloke was wrong, but it didn't warrant your punch as a response.
That's how you ended up here, sitting in your Lieutenant Ghost's office as he analyzes you with sharp eyes.