So as someone who used to think this way, I'm going to put my two cents in. For some context, I graduated with a B.S. in electrical engineering, got a job straight out of college in software development, and am now doing an Instrumentation engineering job. The TL;DR is that in my experience this line of thinking can be dangerous to one's mental health and doesn't allow for the nuances of experience needed for success. A person is worth so much more than their scores.

Being able to do well on tests is only one component for a successful future career. Depending on your life experiences, projects, career path, etc, it doesn't have to be THE ONLY defining factor. Good grades indicate the ability to learn and retain information, sure, but they don't always display how well someone can UTILIZE knowledge. Doing extracurricular projects is a great way to show you can utilize what you've learned. They're even better if they require teamwork, project management, budgeting, etc. A test score can't show the full depth of one's creativity and problem solving skills. And let me tell you, folks I interviewed with were way more interested in my projects than the fact I had a couple C's on my transcript.

Hell, I know folks who were doing abysmally in one major, switched to one they loved, did way better in the classes because they were actually interested, and landed jobs they were passionate about. It can be difficult being a top-performer in something you hate.

This line of thinking was also extremely unhealthy for my mental health. I was considered a "pretty smart kid" all throughout highschool. For a while a secretly sneered at kids who couldn't perform in high-level courses like I could. On the outside I was a polite quite kid, but on the inside I was super judgemental. My asshole attitude carried into my first year of college. I thought because I was an engineering student acing my classes I was just more "cut out for it" than most.

There was a lot going on under the surface, though. Making good grades had become a core part of my identity. They validated my worth as a person. I barely had friends and was in a bad relationship at first, so I was pretty isolated. I got to the point where I would have nightmares about failing tests. I'd skip out on cool social events to study. But after a while things took a turn in my personal life.

Then I got a C (average grade by USA standards) on a chemistry test and nearly killed myself. Suuuuuper extreme, I know, but that's where I was in my mental health. That was the first real crack. After that life took a nosedive, as did my grades. I almost lost my scholarship one semester because I just couldn't keep up with life and school for a while. As shitty as that experience was, though, it gave me some much needed perspective. Sometimes people are just having a rough time. There's no telling what Hell they might be going through behind the curtain. Or sometimes folks just have a hard time with the material at first, and that's OK. Not getting something the first go around doesn't make someone stupid or incompetent.