I came back from a casual ride today. My Garmin uploads to Strava evidently, and I found various segment readings.

What I don't understand about the whole power thing...
I had one 1/2 mile segment, 12% grade. I thought I was going to die. Strave says my result equates to only a 115w power rating, going at roughly 10mph.

Meanwhile, during the same ride, there were other 'segments' with 200+ watt ratings, and I don't even recall them specifically as being difficult.

Can someone explain how this works?