Jim Henson, who was a pretty smart guy, once said…
At some point in my life I decided, rightly or wrongly, that there are many situations in this life that I can't do much about — acts of terrorism, feelings of nationalistic prejudice, Cold War, etc. — so what I should do is concentrate on the situations that my energy can affect.
That's a pretty good quote there…one of the ones I find myself quoting to others a lot these days.