[gen220]

I agree with you, too, that experience helps.

But I think the aphorism covers the case you’re describing too.

It’s possible that your loop is slow, but if you’re working on a program of sufficient size and complexity, you simply won’t know if it’s the bottleneck without using a profiler.

The purpose of the statement is to save you the trouble of 10xing performance of a function, so that it takes .1% of all execution time, instead of 1%. Do sufficiently complex programs, and without a profiler, you won’t really know if a loop is taking 1%, 10%, or 80%.