Oscar Wilde put this line in Lady Windermere's Fan in 1892, in the mouth of Lord Darlington, a minor aristocrat whose job in the play is to be witty and slightly dangerous. Wilde wrote it two years before his own arrest and ruin on charges of gross indecency, which lends the joke a retrospective weight it did not originally carry. He was warning everyone, including himself, and nobody listened, including himself.

The line is usually treated as a piece of decorative naughtiness. It is actually a precise description of a real failure mode. We carefully resist the things that cost us nothing to resist: the second pastry we did not want anyway, the meeting we had a reason to skip, the opinion we were never going to hold. When the actual temptation arrives, the muscle has been practicing on weightless equipment. The no collapses at the moment it was needed.

A cat poised with one paw above a glass of water sitting too close to the table edge is the pure, frictionless version of this. There is no reason to push the glass. There is every reason not to. The paw goes forward anyway. The temptation is the whole architecture of the moment. Wilde, who would have recognized the cat as a colleague, was never really joking. The glass, inevitably, goes over.