Before you've gotten a firm grasp on the subject, you might be convinced that your answer is right but it's not. Especially when the maths becomes more complica

Before you've gotten a firm grasp on the subject, you might be convinced that your answer is right but it's not. Especially when the maths becomes more complicated. If nobody tells you it's wrong, you will incorporate more and more wrong things in your understanding. I notice this horrible effect every time I'm solving exercises for uni and there are no solutions. I think I've done good work. Sometimes, everything really was right, other times, I made fundamental mistakes all across the exercises, showing me that I didn't understand something important. Of course, when you're in research, there's no key. That's why it's so difficult. But it doesn't make sense to reinvent the wheel, as in, researching things that are already well known.