If you really have a loop that is reading from a database at 100ms each time, that's not because of not having optimized it prematurely, that's just stupid.
> look, I'm sorry, but the rule is simple: if you made something 2x faster, you might have done something smart if you made something 100x faster, you definitely just stopped doing something stupid
I think there is just a current (I've seen it mostly in Jr engineers) that you should just ignore any aspect of performance until "later"