Typical junior manager behavior. Assuming that my coworker and girlfriend aren't lazy or incompetent and are acting in good faith, what might be the cause of t

Typical junior manager behavior. Assuming that my coworker and girlfriend aren't lazy or incompetent and are acting in good faith, what might be the cause of the managers behaving this way, and how can they manage the situation for less frustration? The "cause" here in the simple fact that the manager in this case doesn't really know what they're doing. Which at the bare minimum should include: (1) the ability to reasonably predict whether someone can complete a given task, and (2) the ability to trust people. This "trick" used to really annoy me many (many) years ago the first time it was pulled on me. Now I just go "okay - another junior / insecure manager" and go on cashing my paychecks / looking for a better job. Being as this is all their problem, not mine.