Regret for the things we did can be tempered by time; it is regret for the things we did not do that is inconsolable.
-Sydney J. Harris
I know two things about Sydney J. Harris: the above quote, and that he ended up on Nixon's shit-list Mark II. Those are enough to make me like him a lot.
This quote has very serious overtones - when I think of inaction in the face of injustice, especially. But it also correlates well to "It's better to ask forgiveness than permission," which are words to live by when you're trying to get something done in a corporate setting. That makes this an all-purpose quote. Use it well.