There is a very important reason for this.
Firstly, muscles grow because of an adaptive response to the environment. You out your muscles under stress by lifting weights, and as a natural response to that stress the muscles grow larger and stronger. This is a hardwired evolutionary response that we al came built with, a survival mechanism.
Let’s take your typical Joe from the gym for example. Joe goes to the gym and decides to work on his chest. He loads up 175 pounds, and reaches muscular failure on his last set (He couldn’t do any more reps). He subjected his chest, shoulders and triceps to a stress level of 175 pounds for X repetitions. His body perceived this stress as potentially harmful to its survival, and as a result, if he provides his body with the necessary tools (such as protein, water, and carbohydrates); his body will take those materials and use them to build the necessary muscle tissue to adapt that load.
So Joe is happy with his workout, he properly stressed his by training to muscular failure, he consumed the necessary nutrience needed to produce growth, and now he can expect to get bigger and stronger as a result. By the time Joe’s next chest workout comes a few days later, his chest, shoulders, and triceps will have had the necessary time needed to recover from the stress that 175 pounds for X reps produced. He will now be ready once again to put his body under more stress. Now if you have been paying attention you might be able to see where I’m heading to. 175 pounds has been adapted to. Joe’s chest, shoulders and triceps now become slightly bigger and slightly stronger then as a result. Here’s the bottom line. Joe’s chest, shoulders and triceps will only become even bigger and stronger when they are presented with a stress level that is greater then the last workout. Either more then 175 pounds or more reps then the last workout. If he presents his body with the same stimulus, nothing new will occur, and will remain the same size, the same strength, and his gains will not move forward.
A lot of bodybuilders and people at the gym don’t track down their workouts or they just forget all together. Joe goes to the gym and has allowed his body to recover from the previous stress level he had for his last workout and can’t even remember the weight or reps he performed from before. How can he possibly have any idea what he needs to do in order to stimulate new muscle growth? What happens if he sets up the same weight as the last workout by accident, or performs the same reps or less then the previous workout? What happens is Joe waists an opportunity to stimulate new muscle growth and new strength gains. Not only that but he waists his own time, his own focus and accomplishing close to nothing. If he does not present his body with a stress level that exceeds the previous workout, he doesn’t gain.
Now here’s the thing. Most people do progress in the long run. As the weeks and months and years go by most people get stronger and push more weight and they do move forward. But they don’t do it with precision, in other words they don’t write down and track their workouts and because of this they progress much slower then they would if they did write it down. They progress in the long run, but they still have weeks and days where they do the same things without noticing it, or they might even move backwards. All those days and weeks are wasted opportunity. Let’s face it; if you enjoy putting yourself through pain and discomfort in the gym, without getting anything out of it, then that’s you choice. If you’re like 99% of the population out there, your goal is to gain as much as possible in the shortest period of time while exerting the smallest effort possible.
This seems too simple and yet many people ignore the basic laws of progression. I see too many people arguing about the best way to train. Exercise selection, rep range, rest between sets, work out length etc, but underneath all of this, underneath each specific workouts, the law of progression is absolutely universal. You might also find it motivating to actually see in concrete writing how much you have progressed, and where you stand now.
If you have read this far, then I hope I have convinced you to track down workouts, since in my opinion this is the most beneficial way for gaining muscle and the best worth of your time.