The other thing people struggle with is frequency. If an activity carries a 1 in 1,000 chance of an accident, that might be ok as a one-off, but if you had to do that activity....I don’t think it is as clear cut as that with outdoor activities ....
Good point made, but Pete's point rings very true for me. When faced with a challenging climb underground, I always like to have a go. I'm not a great climber, and I certainly don't want to hurt myself, but it's, well... more fun.
Others I cave with, whom I greatly respect, take the approach of 'If I've got a rope, then I'll use it, even if it's not strictly necessary, because it's safer'.
What's the difference? I think it's because I don't cave that much, so every underground trip is still a bit of an adventure and a 1/1000 risk seems acceptable.
For those who cave much more frequently (who are no doubt fitter, better and safer than me) a 1/1000 risk is too high - if you do 50+ trips a year, then a bad outcome becomes more likely.