"By deliberately limiting the irrelevant things you do and think about, you automatically become much, much better at the relevant things on which you spend your time."

How Big is your Circle of Control?: "You will have a much better life, if you focus your mental and physical energy ONLY on the things you can personally influence. Everything else is a distraction that pulls you away from running your life properly. But quite counter-intuitively, this smaller focus does not shrink your influence and your ability to do good. It causes these things to increase. Covey calls the range of everything you spend time thinking about your Circle of Concern. Similarly, everything you can actually influence is called your Circle of Control. For most people, the two circles look like this:

"But what will I do, if I’m not busy being concerned with things outside of my control? 

Now here’s the reason this counterintuitive mind trick works: By deliberately limiting the irrelevant things you do and think about, you automatically become much, much better at the relevant things on which you spend your time. The increases in your health, wealth, focus, network of friends, and knowledge of relevant things from reading library books and talking with other Highly Effective People will have the following effect on your circle of control"