If you do good, people will accuse you of selfish ulterior motives.
Do good anyway.

Source: Taken from a line in the poem The Paradoxical Commandments which he wrote as an undergraduate at Harvard.

Comment: In 1997, Keith learned that the poem "The Paradoxical Commandments" had hung on the wall of Mother Teresa's children's home in Calcutta, India and, two decades after writing the original poem, Dr. Keith wrote a book of the same title expanding on the themes of the poem: Anyway: The Paradoxical Commandments: Finding Personal Meaning in a Crazy World.

Sourced here with appreciation from Wikipedia