Basics (Weights and Bodyweight)
A very young boy who is enthusiastic about muscle-building will likely attempt to pick up any seemingly heavy object at sight. In his mind, he cares not about repetitions, but whether is strong enough to lift the object. Even when one has a barbell before him, his concern, at first, is whether he can get the barbell (with weight-plates inserted) off the ground or not (safely, that is), before thinking about the number of times he can lift it up. This is the case when training using external load, and the capability to safely lift a heavy object off the ground satisfies the lifting man.
Now take another young boy who is also enthusiastic about muscle-building, who is asked by his friends if he can do a pushup-- not only will the boy do a single pushup, but will attempt to do as many repetitions as he can to satisfy himself and his friends, for a few repetitions will be of no satisfactory.
A trainee's concern in the face of basic bodyweight exercises such as squats, pull-ups or push-ups is whether he can do many repetitions or not. This is the case with bodyweight training, with bodyweight bodybuilding-- high volume or high repetitions.
So it is there. When we were younger, we could see how things worked, but could not explain them. When you are young without bodybuilding knowledge, you want to lift something heavy but safely at the same time-- that is if you want to lift something. When you are young and do bodyweight exercises, you want to do as many repetitions as you can so you could boast about it. And you are certainly sure that you can build muscle with or without weights. You only doubt when you start hearing people's opinions. When you can also do a lot of push-ups, for example, you start getting bored and stop working out because you don't know what else to do, and though they may have shaped your chest, they get irritating when they become a lot easier. You begin to not know whether you could have done more push-ups or that was really all your effort. Well, we are yet to touch on that.