Courage

Courage is one of three personality traits kerbonauts have along with Stupidity and the hidden "badS" flag. In the game file "persistent.sfs" Stupidity is a scalar value with the key brave.

Personality traits to determine how a kerbonaut reacts to variously lethal flight conditions. These reactions range from 'neutral' to 'happy' to 'inconsolable horror', all displayed by facial expressions and gestures typically seen in IVA portraits in Camera view.

As of version 0.23, experiments with non-badass kerbonauts modified to the four possible combinations of extreme Courage and Stupidity ([1, 1], [1, 0], [0, 0], [0, 1]) revealed that Courage does not control fearful behavior. Both Stupid kerbonauts were blissfully ignorant in the face of danger. Meanwhile, the non-Stupid ones both displayed equal fear of accelerating in a rocket built by KSC engineers at exactly the same time despite having opposite levels of Courage from each other.
Subsequent tests with 0.75/0.25 combinations showed an uptick in fear in the more Stupid subjects, indicating that with awareness comes dread.

The badS flag, however, negates all fear regardless of Courage or Stupidity.