And yes, lack of sleep is a factor. As is a general lack of ability to keep up with all the details of what’s going on.
You don’t have to have gone through this to feel at least a little pity for this parent—you just have to come close once or twice in a lifetime. There are few people more scatter-brained than a parent of a baby—there is just so much distraction. The very nature of being a parent means that your focus is divided from moment to moment—add to that working a couple of jobs and doing without rest. Oh, I know how it might happen. Thank the Lord it never did.
Reason #1 that mothers should not have jobs. Their job is...being a mother.