In 1988, in cooperation with a team of experimental physicists, a Condensed Matter theorist, X, published in Physical Review Letters a crucial experimental result dealing with a revolutionary new theory. The conclusions of the paper were proved incorrect a few months later. I discuss the various factors -- scientific, instrumental, but also psychological, sociological ones -- which led to this blunder. I believe this story sheds some light on the process of scientific discovery, explanation, falsification, confirmation, and errors.