I have read this entire thread, and have read several people talking about how this dive was foolish/impossible. ...
Yesterday's "impossible" is tomorrow's liveaboard. The word itself is just a weak indication of disbelief, nothing more.
Consider Everest. After many failed attempts, people finally reached the summit, but only by using supplemental oxygen.
With oxygen, a big climb became less of a suicide mission, and more of a risky but manageable form of adventure travel.
Interesting facts emerged. Some climbers needed more oxygen to reach a given altitude, some needed less.
Among themselves, the mountaineers speculated that there might be a climber somewhere who was so aerobically fit (or genetically blessed) that he or she could climb any mountain on Earth without using any supplemental oxygen at all.
Decades passed. It became clear that if such a person did exist, he or she would be beyond exceptional. Doctors started saying that the human body was simply not capable. They used the i-word a lot.
You will probably not be surprised to learn that in 1978, two European climbers with great innate athleticism, exceptional climbing resumes and decades of experience at high altitude became the first to reach the summit of Everest using only the oxygen they could inhale from the thin air. Climbers everywhere hailed a metabolic miracle.
We now know that enormous lung capacity is rare, just as it is rare to be over seven feet tall. Rarer still are people with this gift who also have the many years of highly focused training to hone critical mountaineering skills in an unforgiving, low-oxygen environment. Working against those remaining few are the uncountable dangerous situations that maim or kill climbers as they try to acquire experience at greater and greater altitudes. Escaping serious harm to become a true superclimber is as rare as winning a lottery.
Reinhold Messner and Peter Habeler were the first. Many people have had the burning desire to follow in their footsteps, but only a tiny handful ever did.
Was this one man's quest to see if he had underwater superpowers?
Decades of painful experimentation show that bounce diving to extreme depths leads to many unpleasant injuries. Although tolerance varies, no one seems to be immune.
Guy Garman seemed to be betting that he had an unusually high tolerance for rapid compression while breathing helium. The fact that he completed shallower deep bounce dives suggests that there might have been a little bit of truth to that idea.
But since he didn't try to repeat those dives, we will never know if they were a statistical fluke. Did he really have unusual ability, or was he just very careful and very lucky a few times?
Sadly, there is little to be learned from this accident that we did not already know.