You'll be happier if you focus on efforts and attention only on the things you can control....

Each of us has a large number of things about which we're concerned: our health, our family, our friends, our jobs; world affairs, the plight of the poor, the threat of terrorism, the current political climate. 

Within that Circle of Concern, there is only a smaller subset of things over which we have actual and direct control, such as how much we exercise, what time we go to bed, whether we leave for work on time; what we eat, where we live, with whom we socialise. 

You'll be happier and more productive if you dedicate yourself to your Circle of Control and ignore your Circle of Concern.

Excerpts from "My life philosophy: 50 lessons from 50 years"