Exactly. If you're building a todo list maybe you can ignore complexity, but if you're working on a data pipeline and you ignore (at least an intuitive sense of) O-notation, it will bit you in the ass.

People also use the phrase "premature optimization" to make a perfectly accurate observation about eager, costly optimizations which may be obviated by changes or have no meaningful relationship to any business need.

Is there really any good reason not to focus optimization on areas it will make a difference, and guide it with actual profiling results?

This. I can't comprehend it when people use sort() to find the min/max element instead of a linear scan. And yes, I've seen it happen.

That's not a particularly bad example, only O(n) vs O(n logn).

So Donald Knuth was trying to get out of understanding computers, got it.

The actual quote reads: "We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil."

O(n) vs O(n^2) is not a small efficiency for non-trivial data sets. This is the point that was being made. Many people forget that the quote hinges on the word "small" and then use that as an excuse to disengage their brain when it comes to basic things.

That's an extremely simplistic, sort of childish response. No one besmirches Donald Knuth.

Taking a quote, out of context really, and using it everywhere as some sort of justification, nay, an unthinking reflex, is, indeed, using it as a crutch.

99% of everything is CRUD