The ones I find most T-shirtable are “Most haystacks do not even have a needle”, “Things are only impossible until they're not”, “The truth will set you free. But first, it will piss you off”, “Reality is not optional”, and “The best way to escape from a problem is to solve it.”

(Note how the first two send apparently contradictory messages. The next twos seem to be variations on the Litany of Gendlin; they remind of something I've read somewhere, “Deal with reality or reality will deal with you.”)