I think it's simple and then, it isn't. The big problem, to me, appears to be people thinking they are eating big and lifting big when, in fact, they aren't.
Once you get that concept down and can pack on, say 15-20 pounds, then you are likely at a point where you might want to being a deeper understanding of how your body responds to training frequency/volume and how you might need to tweak meal timing and/or composition.
All very simple AND very complicated.
Complication makes it easy to explain failure.