Courage

The Courage value of a Kerbal determines how they will react upon specific events occouring around them. If there is a high courage value and part of the ship explodes, for example, they will not begin to flail and yell as they usually do, but will instead laugh it off and continue with their now more dangeorus and infact mabye life threatening mission as before. It is closely linked to the stupidity value, and since they appear to be like a scale (High stupidity, low courage and vice versa), it can be assumed they work the same way.