I would also add that person who becomes craven on battlefield, suddenly becomes craven in every aspect of his life. I previously wrote that I wasn´t allowed to kill boar when I was hunting, when I was informed about stag being in the woods, I was so afraid that I ran away and when I was making feast for my vassals, I didn´t join performers, because I was craven. But, surprisingly, I could still go to battle and lead my troops there (and since I was awesome commander in every aspect, being craven influenced nothing).
Problem with traits is that they are not complex enough. In real life, I wouldn´t face boar with my spear and I would be terrified in battle, but I would definitely do crazy stuff during a feast. And if I was on hunt, I wouldn´t run away when other people say that there is stag in the woods. Game doesn´t distinguish that. It just considers you craven and that means that you are craven in every aspect of your life, even though you were just afraid in battle. And it still lets you lead troops in battle! I can´t even emphasize, how much stupid this is.
Also, one thing. You all are saying that being in middle of battles will influence you, but what about being commander in battle? You can lead troops without actually being in middle of fighting. You can always be on some hill in back of your army and watch the battlefield, commanding troops from secure position. Not all leaders are Theoden, Robert Baratheon, Aragorn or Jaime Lannister, there are also Tywin Lannister, Menno Coehoorn, Denethor or Stannis Baratheon. Some commanders will just watch the battle and fight only when it is necessary.