To not be alert to an opportunity
If someone is asleep at the switch, they are not taking their responsibilities very carefully or being alert to an opportunity. Another form of the idiom is ‘Asleep at the wheel‘.
Etymology: Describing the situation of someone sleeping while they are responsible for operating the switch (device) that allows a train to move from one track to another.
I was asleep at the switch. I didn’t know about the job so I didn’t apply for it.