Like Drew, genetics for me. I was a slow and clumsy kid/young man at every sport I did until I discovered I could climb. I"m a mountain goat. Good for very little else. That discovery drew me into racing. (That and the ability to draft.) Now, many years later,it is still my joy. I am doing far less climbing this year, but that is because I am going through PT so I can get back into riding as I love for the rest of my life. (Achilles, etc.)
Ben