Word for being not brave enough or too brave
Someone having an inappropriate amount of courage (or any such relevant quality) while dealing with a situation is naive (likely due to inexperience).
He didn't win the dragon because he was too naive.
ODO:
naive
(also naïve)
ADJECTIVE
1 (of a person or action) showing a lack of experience, wisdom, or judgement.
‘He has been particularly criticized for lack of military experience and naive views of warfare.’