Premature optimization is the root of all evil.
In my line of work, it is sometimes invoked as a sort of apology; an excuse for why more time wasn't spent on performance: "This sucks, but at least we didn't.....prematurely optimize!"
My job is to fix performance issues and help other developers write well-performing code, so I'm not a huge fan of this quote. We shouldn't let an out of context quote guide our development strategy, no matter the source!
When things bother me, I like to stop to take a closer look. Here's the full quote:
We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil.
I translate this to: "When optimizing, don't get distracted by things that don't matter."
I would never translate this to: "Hold off on optimizing things until it really hurts."