fall asleep at the switch
fall asleep at the switch {v. phr.}
To fail to perform an expected task; be remiss in one's duty.
The two airplanes wouldn't have collided, if the control tower operator hadn't fallen asleep at the switch.
The dean promised our department $250,000 but the foundation never sent the money because someone in the dean's office fell asleep at the switch.
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Source: A Dictionary of American Idioms
