I am more along the line of thought that the culprit is most often under-recovering. But that, like most everything else, is a very individualized situation. Everyone will require different levels of exertion and recovery to reach their optimal performance.
I tried to train in my younger days with little or no progress. While I was lifting, I was always either playing sports or doing insane amounts of cardio in the Marines. I had actually convinced myself at one time, despite always being a large dude, that I was a "hardgainer".
When I decided to make this last run at lifting I did a lot of research. This time I convinced myself that I had previously been overtraining.
After analyzing everything I have done this time, and the progress that I have been able to show in just 6 months of training, Strongly believe that I was under-recovering. I changed a lot of things this time around. Though it was unintentional, almost everything I changed had to do with recovery.
I (massively) increased my calories instead of reducing them. I became anal about getting 8-10 hours of sleep EVERY night. I don't train if I feel unrecovered. I don't skip the workout, I just move it back by a day.
I consistently train above 85% of my 1rm weights on nearly every exercise. I have had no problems this time around. In fact, in just six months of training, my current bench press is well above my previous best SQUAT (and I won't even mention how much it is over my previous best bench press, lol).
So, I believe that it comes down to recovery. Some folks require more recovery or less exertion than others but, when you find where YOU need to be, it will be golden.
It all comes down to "How much can you do and still be able to recover from it before your next session?". It will be different for everyone but that, in my opinion, is the magic formula. It is a three pronged attack that requires one to "study" themselves and learn how to read the signs.
That's just how the fat guy sees it. lol
Ye olde natty fatty goals:
#1-compete in a pl meet
#2-get a 3/4/5 in the gym, then at a meet
#3-get a 4/5/6 in the gym, then at a meet
#4-set/break at least one state record