To train your courage, you must first be scared.
This isn't to say you'll be apprehensive, although you might be. You must make your choice already haunted by the possible consequences. You need to know what you're agreeing to, all of it, and everything that happens afterward, before you do it anyway.
You will find yourself at the end of your options, not because desperation builds courage, but because a scary thing will exhaust all other options first. Nothing else would be right, and inaction wouldn't be right either.
You will face your task without friends or family. It's unlikely they've abandoned you, but they will not understand, I think. Your mentors and peers will understand how you made the decision, but not why. Some may even imagine themselves making a similar decision, but far fewer will find themselves doing so.
You will face an unfamiliar situation.
You will not be prepared.