After you have done a lot of electrical design-- and probably other types of design, you develop a good "data sense", and also a "timing sense". The data sense is attuned to what adds value to the design. You do not want to put too much detail or unnecessary data, but you want to present the design so that it is right, easily understood, and will not generate questions. Also you want to do things the simplest way. There is also an art of optimizing your workflow to minimize chances for error as well as get things done easier and quicker. The "timing sense" is kind of equivalent to a quarterback who, after a certain time, starts to feel that he REALLY needs to get rid of the ball. If you have done enough designs you know when you should be done, and can get kind of irritated when you are not.
In short, you develop good skills in facing up to, optimizing, and handling data.