What can we learn from extreme sports enthusiasts?

If you've seen the latest Mission: Impossible film, you'll know that 62-year-old Tom Cruise hasn't let his age stop him from performing death-defying stunts. 

Both on and off-screen, the actor is known for embracing extreme adventures.

So, why do some people love the thrill of extreme sports like sky diving and free climbing... while others shy away from roller-coasters?