fall asleep at the switch

[fall asleep at the switch] {v. phr.} To fail to perform anexpected task; be remiss in one's duty.

The two airplanes wouldn'thave collided, if the control tower operator hadn't fallen asleep atthe switch.

The dean promised our department $250,000 but thefoundation never sent the money because someone in the dean's officefell asleep at the switch.