asleep at the switch

{adj. phr.} 1. Asleep when it is one's duty to move a railroad switch for cars to go on the right track. * /The new man was asleep at the switch and the two trains crashed./ 2. {informal} Failing to act promptly as expected, not alert to an opportunity. * /When the ducks flew over, the boy was asleep at the switch and missed his shot./