I would argue that sometimes students are right when they complaint about a subject being useless or obsolete (e.g. our network professor told us everything about the OSI protocol stack in great detail, and barely touched TCP/IP), but most of the time they don't know what will be useful later in life.
On the flipside you can take the most essential, practical and important topic and deliver it with such dullness that everybody falls asleep.
The first step in teaching (IMO) is to make people interested to hear what is being said. If your subject is useless and boring to most people you have to find a way to make it useful and interesting to them. This requires rethorical and social skills, good presentation skills and a deep understandingnand interest for the subjects to be thought.
In reality most subjects have interesting bits, but is the task of the teacher to make them relate to the world. If your prof thougth you about the OSI protocol stack so long everybody forgot its practical applications and how it binds together with higher level stuff, that is certainly knowledge, but it doesn't help you making it part of your understanding of the world.
Imagine that all we were was measured by the salary that we make and not humans and human civilization. Might as well just hand over our lives to the robots now.
But I wouldn't be able to tell if some of the mental agility I have today (beyond languages) could be attributed to the fact that I was exposed to this language which differs from my first languages in multiple ways. The lessons you may take away from any given subject is not necessarily limited to its raw content.
This is a quite known topic in educational sciences, e.g. when answering the question why it still makes sense to teach kids how to do maths without a calculator in an age where you have it always in your pocket — that is because it (A) forms an intuition about mathematical correctness and (B) logical and numerical thinking gets trained as an side effect.
Ofc all of that doesn't happen when you are unlucky enough to have had bad teachers, but that wasn't the argument.
So you also have to wonder how many potential math prodigies we've missed out on, simply because they had a bad maths education at school.
- How and when would you know a subject doesn't click? In my case German (my first language) and English sucked for roughly 8 years. I ended school with A in both and was the only student in my school without a single mistake in my exam.
- School gives you good grades if you managed to learn the topics at hand. Being able to learn what is needed or what you are bad at — not what you want and are good at is a skill in itself that can be important in life. I'd argue unless you are an exceptional genius (unlike 99,999% of pupils) you gain more from pulling through than you would if you called yourself a genius and focused on a single topic. Schools goal is to educate the majority
- pupils (and often also their parents) are utterly unable to judge which bits of school will be essential to their later life. I had many collegues who utterly hated every second of a multitude of subjects, only to years later tell me how glad they are now to have had been subjected to it (which brings me back to my first point)
We could (and should!) argue on how school works as a system of grades, teachers and pupils — ideally teachers would motivate students to become curious about and proficient in subjects without the motivation of good or the threat of bad grades. But if my experience as an educator at the university levels (without grades in mh case) shows one thing it is that those first semester students who are really able to judge what will be useful to them later on are not many. Many of them are more like the dog in the meme: "Only stick, no take" — they want to be able to do the cool thing without knowing what is needed to do the cool thing.