William Stone quotes:

Many people think all I do is some random engineering work in between caving expeditions. It's been far more deliberate than that.

Cave divers, of course, deal with an elevated level of risk, and the most that I can say here is that we tend to conduct our work at the bottom of a deep cave on an extremely conservative basis with heavy levels of backup equipment and a policy to abort if any single person doesn't like the situation underwater at any time during the mission.

Generally speaking, moving water is the most dangerous thing you can encounter underground.

Caves are whimsical things, and geology on a local scale is random and unpredictable.