A gamer superstition. The Desire Sensor detects what
rare item, or event you are
farming for, and prevents the
game from giving it to you. Only when you forget about it, or no longer need it will the item drop, or event happen.
"Holy shit the Godsword Dropped! I remember
running this dungeon for months, and I never got this damn
thing. Of course now its
worthless. Friggin Desire Sensor, why do you tease me so."
-MMO player's lament