You think a normal thing to do is :
Have course work and learn all about it , probabl do really well on it and go to the test and get like a decent mark. Get a few questions wrong and looking back over it your like "**** I know that" but oh well ! I have a A on my course work and a B/C on that test . Should avarage out as a A
What actually happens :
Learn the stuff and about 2% of the course work is acknowledged stay up till countless hours revising from year 9 and only just get a pass cuz of the new GCSEs and you probably got the same question wrong even though you know how to do it , your just rubbish under tests. Then you can't get in to the uni you wanted cuz of the one question you got wrong in the GCSE , but given it now you probably could of done it. But yeah , you don't need to know the a2 + b2 = c3 for this job and uni you want