When I was in high school I was convinced I could trisect an angle using compass and straightedge, and I told my math teacher so. He just smiled and said "Prove

When I was in high school I was convinced I could trisect an angle using compass and straightedge, and I told my math teacher so. He just smiled and said "Prove it." He was a good guy. Took me several days to finally understand my mistake, but afterward I had a much better understanding of the problem