If courage is a trait built into each of us, what builds it?

I want to say from genes. Obviously. But I can't deny the feeling that it may be something else. Maybe an Astrological planetary conspiracy. Or perhaps even higher than that.

I kind of have to wonder if it's sometimes just fearlessness that's built up by lack of concern or by fighting bigger monsters. 

Self belief...

Practice, good luck and survival.  

Hmm. I think that both of those situations would create a certain thick skin that would make little monsters and apathy, easier to fight. Or fight them with less fear. The proverbial nowhere to go but up. The had enough effect maybe.
Then again those things, while they may make you shine, they may brake me.
I have to think about it more.
I do understand your point. Ty.

fear

we do

I don't think courage is built into us. I think we have to build it as we grow and learn how to deal with adversity.
1. You learn values through education, as through religious classes or parental advice and school.
2. Common sense is built into you and goes along with the other parts that work together to get courage.
3. You build strength through learning how to solve problems.
4. You gain confidence as you learn how to manage your problems successfully.
5. You have a sense of integrity, if your values have served you well. This is your sense of worthiness.
6. You build your convictions about you beliefs and standards.
7. Courage is what you have if you are willing to go through all this faith building of your psyche. If you have faith the size of a mustard seed and courage, life will be so much better for you.