Ok this isn't a topic for HN so there is a lot of pseudo-intellectual nonsense in thread. Anyone into bodybuilding understands the following: You have two different types of muscle fibres, fast-twitch fibres and slow-twitch fibres. The fibres that get big from weight lifting are your fast-twitch fibres. Fast-twitch fibres only get get into use when you are near muscle failure (when your slow-twitch fibres aren't enough anymore to take on the load of the weight) or in explosive movement. The goal is to overload your fast-twitch fibres by lifting to near-failure as much as possible so you signal to your body it needs bigger fibres. So you want a good amount of reps and sets in. As for the specific exercise you do, this is generally an art-form. You can do pull-ups or you can do lat-pulls for your back. More importantly you want to overload on the exercise. This can come in the form of increasing weight, intensity or reps than you did in your last session after recovery. You can always change your exercise if you plateau. Beyond that it is just rest, diet (especially protein) and genetics (yes this is a big one). I have continuously gained muscle mass over the past 18 months. Consistency may be more important than anything else.

If you are just training really heavy and doing <8 reps all you are doing is training your strength which is more neurological than it is about muscle mass.

But the number 1 issue I see is that people seem to think exercise is the rocky montage where you just do a bunch of things and get tired or do 100 push ups every day. A lot of pop culture references to exercise look like this. Real world exercise unless you just want to burn calories is much more focused than that but it is also not complicated.