Did you once do someone a favor? You mean once you had the awesome privilege of doing someone a favor? Gevalt!
Rabbi Kloynimus Kalman says, the greatest thing in the world is to do someone a favor!
The Baal Shem Tov says, if once in your lifetime you gave one thirsty man a glass of water, that is enough reason to dance for 70 years! ~ R’ Shlomo Carlebach zt”l