This concept, of striving beyond certainty, has been elaborated on and restated by many notable individuals.

The one that's most familiar is perhaps Eleanor Roosevelt's comment, "If we wait till we're ready, we'll never get started."

The subject came to mind when I read this past Friday's USA Today story about Donald Rumsfeld's testimony before the Senate Armed Services Committee about funding and installing a missile defense system.

Senator Hillary Rodham Clinton said, "It strikes me as a little odd that we would deploy a system that hasn't succeeded and expect that to serve a deterrent value."

Rumsfeld replied, "If you didn't do anything until you could do everything, you probably wouldn't do anything."

I like it.

Rumsfeld's "known unknowns and unknown unknowns" remarks of last year will undoubtedly end up in the next version of Bartlett's Familiar Quotations.