I wish I could go back and thank my GCSE Maths teacher who tutored me individually so that I could get a C in GCSE and do my 'A' levels.
At the time I was thankful, but I didn't realise at the time how much extra work I generated for him marking every single past paper the school had in it's archives.
Maths is still not my favourite subject but I have a solid grasp of numbers which is surprisingly helpful in real life. Never used pythagorus's theorem outside of a math lesson though and I'm nearly forty!