Hey, it takes allsorts, maybe you aren't an adrenaline junky...but need encouragement from friends, etc. Some work better in groups doing daring/hard/different things, others like to go it alone...
I was 4 when I did my first 'stunt'...I climbed to the very top (and it was bending very badly in the wind too) of a thirty foot tree and got stuck...a male family friend had to rescue me...climbing up and pulling myself up was easy, but looking down, whooo! I didn't cry though, I just called for help and was very glad to be able to get down and climb some other trees...
I've fallen out of countless trees and never broken a bone (yet fingers crossed, no broken bones and I am nearly 35!), just been severely winded. I still love climbing trees and would love to go up into a/the rainforest canopy one day...
Then when I was 10 I got stuck on a hundred foot ledge on the edge of a mountain...my dad had to talk me to where they were...without scaring me and losing me to/off the cliff...iff...iff...iff
I have things on this long list that I need to do before I die or turn 50...white water rafting, bungey jumping, hang gliding, base jumping, kite surfing, parachuting...you know the score...and it will get done...mountain biking is now crossed off the list...it's a weekend addition to my usual nonsense.
Life is too awesome to be still too long...ha!