Is there a word for not being brave enough or being too brave? What I'm looking for is a word that combines the meanings of cowardice and foolhardiness, that can be used to describe a person that has a wrong amount of courage; either too much or too little. Example: "He didn't win the dragon because he was too _____". Is there a word that matches my description? If not, why? Thanks in advance.
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.
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.’
I really can't think of a single English word that means both "too brave" and "not brave enough", or "having bravery to the wrong degree", which I think is what you're after.
The closest words either imply a lack of decisiveness - indecisive, irresolute, etc.; fear or cowardice - trepidatious, cautious, nervous, wary, etc; or recklessness - reckless, foolhardy, incautious, etc.
I think you have to decide if he is too brave or not brave enough, and why: is he cowardly, indecisive, or simply cautious? Or is he reckless, foolhardy, deluded or naive? Being forced to choose one of these words improves the description of the character and the situation, so I don't think this is a bad thing.
Reckless: Someone how might be brave (from one perspective) but also naive (from another perspective).
You may also consider the word underestimate, but may require changing the sentence to fit.
Hm... Since you're talking about dragons, you're in the realm of fantasy and possibly world-building. Make up a word! And define it, explicitly or through repeated use in different contexts. I'm thinking of the word "tharn" in the book Watership Down, which describes a particular emotional state in the Lapine language used by rabbits.