Thank you, that is an excellent question!

“Twenty years from now you will be more disappointed by the things you didn't do than by the ones you did. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover.”
Mark Twain

This quote is the first part of my answer and it's a very important part of my journey, so I'm going to add it to the top of the post as well.

The second answer is TRUST. With rock climbing you learn to trust in your belay and know that the rope is there to catch you when you fall. With skydiving I had to trust that I was in the hands of a professional with 4000 jumps worth of experience. With SCUBA you always dive with a buddy that you can trust to be there when you need them.

Lastly remember that no-one experiences "courage", we all experience fear. Then we must choose whether to give in to that fear, or to overcome it.