I didn't used to be afraid, in my late 20s I was a roofer and would throw a flat of shingles on one shoulder, race up a rickety ladder three or more stories, and dance down the ridge line without a thought. Somewhere, I've got a pix of me standing on one leg, full backpack on, on the East Arm of Horseshoe Mesa in the Grand Canyon, probably 800+ foot drop straight down inches in front of me. I was hamming it up for several ladies in my group.
However, something changed in me over the years, nothing in particular happened, but today, I have a hard time getting off a ladder onto a roof only two stories up. I was back out in the Canyon a few years back, and I couldn't get to within ten feet of the edge and my knees started shaking and my sense of balance seemed to collapse.
I've either gotten smarter, realizing how dangerous these actions are and how much it would hurt (albeit, only briefly) to fall. Or, I've become a total weenie. I'm going with the former.
Natch