Where Algebra came to me easily, I had to "work at" geometry and some of the Calculus problems that involved rotating on an axis. When I teach my students, I try to remember how this feels since I am fortunate enough to usually understand most of this fairly fast.
I worked at picturing where and how a shape would end up if changed and it took some time and effort - just like the distributive property did for my students.
Derivatives and such, I absolutely loved.