"With a knight on f8 it can never be mate."--Bent Larsen. (Unfortunately last tournament I learned the magic doesn't work with a knight on f1.)
The other thing I often think of during games is Tal's "What a difficult task it was/ To remove from the marsh the hippopotamus." In context it means "Sometimes you can't calculate it all, just go ahead and sack."
Got a favorite chess slogan or phrase that you like?
Let's hear it. How about:
A knight on the rim is dim. Similar to "A knight on the wall will fall".
Others??