Every time I've been in a cave...
...I've gone through the following thought process:
- Jeez think of all that rock above me. What if it caves in?
- Yeah, but how many millenia has it been here. It would be much easier to win the lottery than to be hit by a cave-in right now.
- Jeez, what if there's an earthquake???
- Well, how many earthquakes has it withstood in those millenia that it took to form and to wait for my visit?
At about that point in the cycle, I'm fine with it, and good to go.