The don't think they are Heroes. They never think the reason they did it was heroic at all. In this case they did it because if they got out alive and he died they could never forgive themselves for abandoning him. They think that keeps them from being heros. They didn't do it for him, they did it so they could live with themselves. They don't understand that is why all heros are heros. It is the one thing that separates the worthless people from the very, very, valuable people.
You can interview a thousand heroes and it is always the same. In war some lowly enlisted man will save a company of men from certain death. He will say I thought I could take that machine gun nest out. If it wasn't taken out most of the comapny would die. I could not live with myself if I didnt't try.
Mark Twain said man is the only animal with a conscience .. and the only one that needs one. In a terribly bad situation, never look for the big, brave and strong. They often will look out for themselves first. They are not likley to help you until you don't need it. Look for someone with a strong conscience. Even a very weak person with a big conscience will always do the heroic thing. It is what all heroes are made of.