Comment by bborud

I went back and had a look at that maxim a few years ago and found that it actually doesn't say what many people claims it says. And definitively not as the blanket excuse for slow code that it has always to some degree been used as.

The reason for the misunderstanding is that the kinds of practices it actually talks about are uncommon today. People would often take stuff written in higher level languages and reimplement them in assembler or machine code. Which makes them more time-consuming to change/evolve.

It also isn't like it is hard to figure out which part of a piece of software that is taking up your runtime these days. All worthwhile languages have profilers, these are mostly free, so there is zero excuse for not knowing what to optimize. Heck, it isn't all that uncommon for people to run profiling in production.

Also, it isn't like you can't know ahead of time which bits need to be fast. Usually you have some idea so you will know what to benchmark. Long startup times probably won't kill you, but when they are so long that it becomes an UX issue, it wouldn't have killed them to have a look.