Comment by ummonk

From my experience it's better to just consider performance from the get-go, and carefully consider which tech stack you're using and how the specific logic / system architecture you've chosen will be performant. It's much easier than being stuck with performance problems down the road that will need a painful rewrite.

The whole mantra of avoiding "premature optimizations" was applicable in an era when "optimizations" meant rewriting C code in assembly.