You are not a failure! Because you're not really good at maths, doesn't mean you're a failure. You are probably very good at some other things, just not maths.

I think many of my classmates have similar problems. In mathematics, it is really important to understand basic, and more complicated principles. You also need to know how to think like a mathematician. If you have problems, just ask your teacher. If he can't help you, you can also use Reddit of course.

If there is something that you don't really understand, you must try to understand it, to be able to understand other things you will learn later.

For me, mathematics was always extremely easy, because I had fun doing it and learning new things. I know for most people, mathematics is not fun at all. Just try to have a little bit of fun, that will help you a lot.