My junior year of high school I took pre-calculus. I did not particularly like pre-calculus--or any math classes for the matter--and yet I took it. My teacher was a very nice woman who thought one thing, said another thing, and wrote an entirely different thing on the board. I liked her, but couldn't understand a word of what she said. Needless to say, it was very difficult for me to understand the concepts of calculus which we studied.
Finishing my homework each evening was, therefore, a struggle of near epic proportions. My father, who throughout my school years usually helped me with math homework, suddenly found himself helpless in the face of matrices, graphs of sine waves, and logarithms. I was equally helpless.
And then one week my uncle and his family came for a visit. This particular uncle engineers rocket boosters, which is quite impressive work. He had always been a bit of a math/science geek, so in desperation my father turned me and my calculus questions over to Uncle, even though Uncle was on vacation. Hope sprang in my bosom, (or somewhere in that general vicinity) and I spread my homework out in front of a kind and helpful Uncle.
Uncle began to peruse my homework with a look of studied concentration, and I'll never forget his next words to me: "Hmmm, I don't know. I haven't done any of this stuff in years." My father and I looked at each other incredulously: a man who builds rocket boosters doesn't regularly use calculus?! The hope in the general vicinity of my bosom began to fizzle out, and a righteous indignation began to build instead. The next day I walked into class and told my teacher, "Calculus is useless. My uncle is literally a rocket scientist, and not even he uses this stuff!"
And that's why (some) math teachers hate me.