I got 100% for my year 8 Maths exam. Topped the year level. Got put into the top Maths groups for ever more.
And then found myself very close to failing year 11 Maths because I was totally unable to understand the work. I'd been memorising and rote learning Maths since Primary school, and by year 11 that just didn't work any more. You needed to understand how to do the work, and I didn't have a clue how you went about that.
No teacher ever picked it up or explained it to me.