From Further Secrets of Adulthood: Be selfless, if only for selfish reasons; be selfish, if only for selfless reasons.
This is a variation of my Second Splendid Truth about Happiness:
One of the best ways to make yourself happy is to make other people happy;
One of the best ways to make other people happy is to be happy yourself.
I have Eight Splendid Truths, in all. (I was inspired by the numbered lists that pop up throughout Buddhism: the Triple Refuge, the Noble Eightfold Path, the Four Noble Truths, the eight auspicious symbols, I decided to dub my fundamental happiness principles as my Eight Splendid Truths. ) You can read them all here.