At the end of this chapter The Ambush the author shares that at times he forgives himself and sometimes he doesn't for killing a man. Soldiers experience a lot of trauma and PTSD from things they've experienced but as soldiers this is expected to just be apart of the job. 
In the chapter The Dentist Curt Lemon got his tooth pulled just to prove that he's strong and fearless which is something that is expected out of soldiers.