It isn't about "micro-optimization", that's just what bad developers use as an excuse for never caring at all about performance. Casey uses the term "depessimization" to describe the process of making a program not run like shit.

Modern computers are ludicrously fast, and modern developers have somehow managed to make them slow.

Regardless, these programs should be spending 99% of their time waiting for user input, but instead they're working data through a mountain of abstraction layers on the faulty assumption that it is a) saving developers' time, and 2) that that is worth much more than user time.