Focus is one of the keys to success. Without focus your attention is divided and whatever your doing won’t be your best work, or your best self. If you wish to be great at something, you must devote all your attention to that.
Which will require you to eliminate less important things. You have to discipline yourself to NOT do things.
You have to consciously say no to things that could be fun or interesting but not necessarily what is going to help you achieve your goals.
Instead of forcing yourself to do more, you are actually forcing yourself to do less.
Its a different side of the same coin