Which subjects you should be studying, but not how to improve your work, or specific areas of the subject you should be focusing on. If I get an A in French, do I just stop studying until I slip down to a B?
I was a teacher for 15 years, and I can tell you that grades are meaningless. A kid gets an A and thinks they're done. They won't even bother to read the feedback to see how they could have improved their work. A kid gets an F and thinks they're done, they give up on the subject and again don't read any feedback.
There's cultural and socioeconomic factors to add in as well. For some kids a grade C is great, for other it means they've failed. What is important is them knowing how to improve, not how they rank against their peers.
You talk about your job, and meeting the needs of your client. Does that mean you don't read or listen to feedback from your client? If you get paid, no matter how badly you did the work just to meet contractual obligations, is that all you care about? Imagine you got paid on a scale, awarded by the client, with an A being the full amount and an F being $0.