It nearly always takes a crisis event to bring out the best in someone (sometimes the worst but usually the best. Most people "rise" to the event and are determined not to let it beat or cow them). This will be true for your characters too. The crises you set up for them are what will test them to their limits and you will really know what they are made of because of the way they react.
Do your characters ever surprise you with what they come out with? What do you think your characters' cracking points would be and what would they do if they did crack? How much courage can your characters discover?