Clearly Pfaff has had a lot of success and is a good coach, but he's also a bit crazy. Some of the things he rambles on about can get really out there and weird. He definitely falls back onto what I call "magical thinking" when he can't scientifically back up his methods. Not that I think his methods are wrong, just that he lacks the background to fully explain "why" they work.
This is a good example. It's probably true in any sport (or business field too for that matter) that a lot of failure is actually due to inability to handle their personal lives in a way that allows the consistent training (or studying or climbing the corporate ladder etc) over years or even decades to achieve the highest levels of succes. However, in this case, it is hard to measure or quantify that. I think Dan is saying what he has observed anecdotally. I think he is probably correct in his observation, but that is just based on my anecdotal experience as well, no hard numbers on that.
Getting hard numbers in this case would be hard since it would require somehow identifying and following nascent talent to see if they flame out or stick with the sport to their maximum potential. Lot's of complications in a study like that.
Think back to high school and remember all the wasted talent you may have observed. For me, in high school, I ran with a 9:01 2 miler who quit running his sophomore year of college because he had trouble finding time to both study and party.
I also ran with a 49 second quarter miler (as a freshman) who quit his sophomore year of high school because the steroids he took over the summer combined with the drinking made him fat and slow.
I had a hs teammate throw 190 in the discus, only to quit his junior year at Cal after failing to throw over 160 with the 2k. I think that was mostly poor training, partially as a result of partying (and partially due to the abysmal throws coaching at cal).
Point is, those are pretty high level talents, certainly they could have continued to make significant improvements and maybe reach elite level in their 20s. But they flamed out and we'll never know.
As a coach, I've seen the same trend. I had a kid last year in vault who had to take care of his alcoholic mom. He could have been a contender at the california state meet, but he had ended up being immensely distracted his senior year with those issues. Hopefully in college this year he can break away from that.
Point is, if you look in your past, we probably all have similar stories of teammates who maybe could have become elite in our soort, but never got a chance to find out because their careers ended early due to non sports reasons.
I think it is rare to see that potentiall elite talent who ended up unable to realize their potential due to injury, etc. I can think of only 1 from my high school teammates compared to 3 who flamed out due to lifestyle.