In the things we have brought with us, the most important lesson that still runs through Tim O'Brien's head today is the importance of friendship. It is extremely important not to take friends for granted, because it is incredibly painful and unhappy without them. It's extremely difficult to even imagine what it would be like to feel like you killed your own friend, and that's exactly how it felt after the war for a long time. He endured the loss of one of his troop members because he was shot while going to the bathroom off the path they were all traveling on and since he was supposed to watch over his troop members, he felt incredibly guilty for a long time. Everything is easier said than done, because a person will never truly know what it feels like to kill someone or lose them, until it happens to them or someone.