This quote is generally attributed to Ralph Waldo Emerson -- research indicates that may be a mistake. No matter who said it, I like it. When I'm feeling like far less than a success, this definition makes me breathe easier:
To laugh often and much;
To win the respect of intelligent people and the affection of children;
To earn the appreciation of honest critics and endure the betrayal of false friends;
To appreciate beauty, to find the best in others;
To leave the world a bit better, whether by a healthy child, a garden patch or a redeemed social condition;
To know even one life has breathed easier because you have lived.
This is to have succeeded.