Why have I always told you that the greatest way to change the world is to secretly commit little acts of compassion? It does not matter that people know what you are doing, but rather that you do it. When a large enough number of people finally do something, or something is done enough times, be it prayer or vegetarianism or whatever, it will then happen everywhere, to everyone. It will suddenly seem just normal. […] You must behave as if your every act, even the smallest, impacted a thousand people for a hundred generations. Because it does.

Thomas "Thom" Hartmann (b. 1951) American broadcaster, psychotherapist, businessman, political commentator

The Prophet’s Way: A Guide to Living in the Now, “The Hundredth Monkey” (1997)
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Often quoted as:

The most powerful way to change the world is to secretly commit little acts of compassion. You must behave as if your every act, even the smallest, impacted a thousand people for a hundred generations. Because it does.