I haven’t always loved mathematics. I distinctly recall being pretty miserable in all my high school math classes and the rote learning they entailed.
I started to feel a call to do it professionally when I took a required course called Discrete Mathematics. This course had no textbook and consisted of the professor writing problems in combinatorics or probability on the blackboard for us to solve as a group. Homework and tests were similar. This was a kind of math that I had never seen before. The problems were deeply practical, such as finding the probably of a royal flush in a fairly dealt deck of cards, but also required clever thinking in order to find the solution.