I've been thinking about going back and finish getting my Advanced Higher recently, since I miss all the focus and precision you get in maths which doesn't really crop up in philosophy.
However, going over some notes a friend lent me I realise none of it makes sense. I tried to go back to Higher-level ... fail. Even Standard Grade is having its confusing moments now.
So, yeah. Tell me stuff you've forgotten that you wish you still knew about