Facing the invading monsters, bloodthirsty aliens and the many threats that companions encounter will mean that the characters are usually fairly courageous to even get involved. However, some people are more fearless, and can stare down a Sontaran in the face without flinching or shout at the Cybermen without worrying about the imminent reprisal.
The Brave trait provides a +2 bonus to any Resolve roll when the character could get scared or need to show their courage.