(Really) Risky Business

To evaluate the risks of underwater-cave exploration, Skiles starts by evaluating himself. He does this by leveraging the "theory of pie." A pie is a metaphor for a diver's maximum problem-solving potential. As he preps for a dive and descends into a cave system, the diver loses a slice of pie with each distraction or setback. An O-ring blows while he's gearing up, and he has to stop and change it: Take away a slice. He accidentally sets his tanks down on a dive light and cracks it: There goes another slice. If he loses too many slices, the diver must quit: He must call the dive. If he doesn't -- if he makes the dive with just half a pie -- he won't have all of the mental resources that he needs to deal with a real underwater emergency.

Skiles first put the pie theory into play when he was 19. He was on a dive with Sheck Exley, a cave-diving pioneer who set numerous world records for deep dives. (Exley died in 1994, while diving below 900 feet in Mexico.) Their plan was to dive into the cave system in Florida's Blue Springs, swim 3,000 feet back into the network of tunnels, and lay 1,000 feet of line. (That is, push another 1,000 feet into the unexplored system.)

"It was a hot day, and I felt really rushed as we geared up," Skiles recalls. "When we got into the system, Sheck started swimming really hard, and I had trouble keeping up with him. My pacing wasn't good that day. Then my regulator started to leak. I could still breathe through it, but it was free-flowing pretty hard. So I flashed Sheck down and showed him that my regulator was bubbling. And he looked at me like, 'Shit, all of my regulators bubble.'

"If ever there was a guy who I would blindly follow no matter what, especially at that age, it was Sheck Exley," Skiles continues. "It was a major embarrassment for me to disappoint Sheck. But I knew that I had lost too many slices. I had to call the dive."

And that's exactly what he did. In a way, it would have been easier to keep swimming after Exley; Skiles didn't want his hero to doubt his skill and courage. But looking back on the experience, Skiles realizes that it took even more guts to call the dive. In the long run, quitting gave Skiles the confidence to push on -- to take on even bigger challenges -- because he knew that he had the mental agility to manage the pie.

Diving Solo: Real Risk Takers Work Alone

Calling that dive was a turning point for Skiles. He knew then that he could never be dependent on another diver. He vowed that from then on, he would take control of his own destiny. He would lead, instead of follow. And he would be relentlessly self-reliant -- even if it meant diving alone.

Skiles went on to rack up hundreds of solo dives. Now, flipping randomly through his logbook, he quickly hits on one of them: 125 feet down and more than a mile back into Devil's Ear. He was underwater for three hours. He used up seven tanks (some of which he had cached on his way in). And he did it all without a dive partner.

For an open-water diver, this is heresy of the highest order. The first commandment of open-water scuba diving is: Thou shalt always dive with a partner. A dive buddy is your backup. Dive buddies remind you to check your depth, time, and air-supply limits. If a regulator blows, they are there for you, and you are there for them. But a buddy can be a liability for a pioneering cave diver.

"A lot of what you learn in cave diving runs completely counter to open-water diving," says Skiles. "Depend on a buddy in a cave, and you'll end up with a double drowning, because each guy is relying falsely on the other. Neither one of you is prepared to deal with an emergency on your own terms.

"In fact, by depending on a dive partner, you increase the risk factor," he continues. "There's this false sense of security that you can push farther, because you've got a comrade right there with you. Well, take your partner away, and judge the dive for yourself. Are all systems go? If your buddy wasn't there, would you still be okay -- or would you call the dive? Even when I dive with other people, I dive self-reliant. We all dive solo -- it's just that there are times when we dive solo together."

When judging potential cave divers, Skiles looks for two critical qualities: alertness and awareness. The two words sound similar, but they have very different meanings. Alertness applies to minute changes and fluctuations during the dive. If Skiles wiggles a flashlight -- the underwater signal for "I want your attention" -- alert divers immediately turn their heads to see if there's a problem. But many times, Skiles violently shakes the light and gets no response. The other divers are so task-loaded -- they're struggling against the current, they're reading their gauges, they're worried about losing sight of the guideline -- that they've lost track of the dive itself.