[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./