When I was in high school on the Main Line outside of Philadelphia, I was very shy. I tried to blend in as much as possible. I didn't want to call attention to myself ever; it was easy to do since the school was so large and had thousands of kids.
One day, I was sitting in algebra, and I just didn't understand what the guy was saying. In my class of 60, someone else usually asked the questions I was unwilling to ask, but on this day, nobody was asking him the question I needed answered. The instructor might as well have been speaking Martian–that's how badly I wasn't "getting it."
I hesitated, but then tentatively raised my hand to get clarification.
The teacher called on me, and I asked my question. You know what he replied? "That is the dumbest question I have ever heard." Now, I understand that sometimes an instructor reaches the end of his limit on what he can take but his response was so unnecessary. As an extremely sensitive person, that was the end of my career in algebra. I immediately transferred into a lower class that was so below me, and I never felt confident enough to take algebra again until college.
The funny part? I did so well in algebra in college that the school asked me if I'd like to be a tutor for others.
I have never forgotten that day.