Rule 3 gets me into trouble with CS majors a lot. I'm an EE by education and entered into SW via the bottom floor(embedded C/ASM) so it was late in my career before I knew the formal definition of big-O and complexity.

For most of my career, sticking to rule 3 made the most sense. When the CS major would be annoying and talk about big-O they usually forgot n was tiny. But then my job changed. I started working on different things. Suddenly my job started sounding more like a leetcode interview people complain about. Now n really is big and now it really does matter.

Keep in mind that Rob Pike comes from a different era when programming for 'big iron' looked a lot more like programming for an embedded microcontroller now.

I actually disagree with Rule 3! While numbers are usually small being fast on small cases generally isn't as important as performing acceptably on large cases. So I prefer to take the better big-O so that it doesn't slow down unacceptably on real-world edge-case stresses. (The type of workloads that the devs often don't experience but your big customers will.)

Of course there is a balance to this, the engineering time to implement both options is an important consideration. But given both algorithms are relatively easy to implement I will default to the one that is faster at large sizes even if it is slower at common sizes. I do suspect that there is an implicit assumption that "fancy" algorithms take longer and are harder to implement. But in many cases both algorithms are in the standard library and just need to be selected. If this post focused on "fancy" in terms of actual time to implement rather than speed for common sizes I would be more inclined to agree with it.

I wrote an article about this a while back: https://kevincox.ca/2023/05/09/less-than-quadratic/

My father did some programming in Fortran and Assembly of various flavors. He was always partial to lookup tables where they could replace complicated conditionals or computations. Memory was precious in his day but it could still be worth it if your program did something repeatedly (which most do).