A manager's main responsibility: good taste
It occurred to me recently that, other than (as always) being smart and getting stuff done, you only need one main rule to decide if someone should be in charge of something: good taste.
Of course, nobody has good taste in everything. Depending what you're in charge of, you need to have good taste in different areas.
Code architect: Needs to have good taste for design and architecture. Obviously. But note the difference between this and coding it all himself; if the architect can tell you you're wrong before your mistakes bite you, he's paid for himself.
Project manager: Needs to have good taste in project schedules. This isn't the same as making good project schedules! It's been widely acknowledged by now that the only person capable of estimating a knowledge worker's schedule is that worker. But you still need project managers to assemble all the information, track milestones, and so on. The key role of such a person is to tell you if you're just plain doing it wrong, as most people unwittingly do when making a schedule. Only a person with a taste for schedules can do this well.
Product manager: Needs to have good taste for user requirements. They don't necessarily have to understand the user (although that's the most obvious way to do it); they just need to understand what a real user requirement looks like, as opposed to a pretend one. When you propose a new feature for your product, they need to be able to see why you're proposing it: for a good reason or a bad reason. If they're good at detecting that, then their product will be good.
Team/HR manager: Needs to have a good taste for team members. If you choose the wrong people for your team, it'll be a failure every time; if you choose the right people - the people with good taste - you have a much better chance of success.
Good taste is critical, and there are a million forms of good taste. Right-thinking people can disagree on what they like or don't like. But right-thinking people are also pretty good at discarding the vast majority of stuff, which is tasteless and appeals to no one.