“Your only obligation in any lifetime is to be true to yourself. Being true to anyone else or anything else is not only impossible, but the mark of a fake messiah.”

Source: Eat, Pray, Love

Letter to Michael http://www.lettersofnote.com/2011/01/dont-do-it-for-anyone-else.html

Source: Letters of Katherine Anne Porter

Source: Fruits Basket, Vol. 8

Emperor Has No Clothes Award acceptance speech (2003)
Context: Schizophrenics have a whole lot of trouble telling the level of abstraction of a story. They're always biased in the direction of interpreting things more concretely than is actually the case. You would take a schizopohrenic and say, "Okay, what do apples, bananas and oranges have in common?" and they would say, "They all are multi-syllabic words."
You say "Well, that's true. Do they have anything else in common?" and they say, "Yes, they actually all contain letters that form closed loops."
This is not seeing the trees instead of the forest, this is seeing the bark on the trees, this very concreteness.

Source: The Portrait of a Lady (1881), Ch. XXIII.

As quoted in "The Vindication of Edwin Land" in Forbes magazine, Vol. 139 (4 May 1987) p. 83; this was later humorously altered:
Don't do anything that someone else can do. Don't undertake a project unless it is manifestly important and nearly impossible.
Edwin Ladd, Department of Astronomy, Harvard University (August, 1990), as quoted by Lincoln J. Greenhill at Harvard University http://www.cfa.harvard.edu/~lincoln/