I run processes where one missed reading or one wrong valve could set off a real disaster. So I stay sharp every second of every shift, because the moment I don't is the moment something could go terribly wrong. Holding that kind of watch, day after day, is a strain nobody outside really sees.
More people experience this than they realize.
One lapse could cause a disaster, so you hold constant vigilance shift after shift.
If this sounds familiar, the Library can help you find the bigger picture.