It's literally Donald Knuth:

“The real problem is that programmers have spent far too much time worrying about efficiency in the wrong places and at the wrong times; premature optimization is the root of all evil (or at least most of it) in programming.”

Knuth would fail the technical interview.

Can you give some examples of such products?

A database would be an obvious example. Analytics platforms and message queues are another couple that come to mind.

You can't patch the kind of performance you need for these products after the fact, it needs to be baked into the architecture.

I think the authors above just meant that you don't know if your product will even get there so instead of over-engineering your stack and prepping for every possible scenario you'd take Just-in-time approach and conquer the problems when they come at you.