When you are trying to improve your ability to grow muscle, improving your execution is absolutely fundamental. The foundation for all other physique based training comes from execution. You have to have the skill to contract the muscle you want and keep tension in the muscle under load and fatigue. If you have never taken the time to slow down and focus on feeling the working muscle, you may be very poor at isolating it.
The body naturally adapts to learning movements unconsciously. Just like throwing a ball, after you have done this a few times, you do it without thinking. Isolating and overloading a single muscle is not a naturally learned motor pattern. In terms of your biology, you body would much rather disperse load among different muscles and levers to make the movement as easy, and little energy demanding as possible. When you are trying to grow muscle, this is the opposite of what you want. You want to force the targeted muscle to do as much of the work as possible and expend as much effort and energy as possible.
You don’t naturally develop the ability to isolate muscle well. You have to train this skill meticulously. This requires you to slow down, use a slow controlled tempo, lighter weights, and work at the pace in which your mind muscle connection can improve. Holding in the short position and squeezing the muscle as hard as possible is (called an isometric) great for developing that connection to the muscle. But once that skill is developed you have to put on your boots and go back to work.
But how do you know when you are ready to graduate from learning how to contract a muscle to progressing the intensity of those contractions. This may differ from body part to body part and exercise to exercise.