There is always one trick

Over the last few weeks I've witnessed a number of games that have ended in disaster for the player who was nominally winning. As a result I've come up with yet another chess adage, to be used when your opponent is playing on in a worse to losing position. "There is always one trick".
The point of saying this to yourself during the game is to force you to actually look for the trick, rather than just blindly following your "anything wins" plan. If you can see the trick, then obviously you can take steps to avoid it.
An example comes from the game Feuerstein v Mednis 1957. In the diagrammed position Mednis had just played a3 and offered a draw. Feuerstein refused the draw (correctly) but failed to look for tricks in the position. Obviously the pawn wants to queen, but is covered by the rook and the bishop. The rook has to move, but if moves along the file then it is only the bishop covering a2. There is also the fact that Black can also play Bc5+. If White had added all these ideas up, he may have spotted what Black was hoping for. Instead he played Rb7??, walking into Bc6!! which wins on the spot. Rather than win, or even draw, Feuerstein had to resign instead.