If we could change ourselves, the tendencies in the world would also change. As a man changes his own nature, so does the attitude of the world change towards him… We need not wait to see what others do.
— Mahatma Gandhi
The title is the more often quoted, though it seems there is no evidence he actually said it. The closest he did say is the quotation above. Makes the same point, and sounds less like a soundbite :)
Image: By NASA [Public domain], via Wikimedia Commons