Computers. How they have changed our lives.
I recall being informed when I started college that I was going to have to take a few courses in computer languages (versions of COBOL and FORTRAN). I thought that was pretty useless. After all, I was (literally) the first person to use an HP-35 calculator (patent to be applied for) and not be stuck with a slide rule. (OK. Brooklyn Poly made me learn how to use a slide rule, anyway.)