Why is it so hard to conquer FEAR

When we have fear and walk through the fire of fear we usually realise that there was no fire and walking through it was the best thing ever. 

So why is it sometimes so hard to conquer fear and just do it? Why do we give up and fall into frustration and sadness? Is there something in us programmed that we can change to not fear the fear so much? Where is this fear of the unknown coming from and how can we just let it go? 

thank you 🙏🔥😁