divestoclimb
Contributor
Tom Mount will tell you most of this is common sense. Some have it and some don't.
There are some divers who are smart, careful, intuitive, and could do most deep trimix diving or long cave penetration with a minimal of formal instruction.
There are others who could spend a fortune on classes and equipment and never have the skill set, situational awareness, or common sense to be in a swimming pool, much less a cave or wreck.
My thoughts exactly. I didn't need a wreck penetration or drysuit class, I figured it out on my own, read some books, used my other training/experience (cave), dove with people more experienced than I was, and approached it conservatively. This is how people learned before all the courses came about. I wouldn't recommend that approach for everybody, though, and not for cave or CCR's under any circumstances--history shows that learning those activities from scratch killed a lot of people. The problem is we have more and more people entering tech diving who...well... don't fit the description "smart, careful, intuitive" (and I'd add that they need good judgment).
This article (The Wetware Crisis: the Expert Pool : Bruce F. Webster) gives a good theory behind this. It's applied to IT and computer science, but I think it applies to us too: there are about the same number of good tech divers entering the sport per year as there used to be, the problem is the total per year has gone way way up.