I don't know the answer. Not for you. Barely for me. Except that it's my life, so I'm experimenting on myself. Fine tuning the dial. Sometimes I get it wrong and I've just plain suffered and am unhappy. But other times ... make room for my joy.
What was I doing standing on the starting line of a 50-mile race? To be honest, that question never crossed my mind and I suppose if that seems like a logic question to ask then you probably don't understand why I stood there.
I wish that I could say that becoming an ultrarunner came with some poetic philosophical realization, and I'm sure there's a lesson to be found somewhere. But, I'm not going to dig for it. I'm just going to take a deep breath, and keep on putting one foot in front of the other.