Math has always been easy for me but Differential Equations was the only class I ever flunked
I took it as a 'Self-Study' class that I thought would be easy. I did the self part, but not the studying part and flunked
So 2 years later at the end of my senior year I still had this Diff Eq class hanging over my head and had to take it in my last semester. That was tough having not had any pure math classes for 2 years!