Related:
“premature optimization is the root of all evil”
vs.
“Programmers waste enormous amounts of time thinking about, or worrying about, the speed of noncritical parts of their programs, and these attempts at efficiency actually have a strong negative impact when debugging and maintenance are considered. We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil. Yet we should not pass up our opportunities in that critical 3%.”
I frequently see people use that cropped quote to justify paying no attention whatsoever to performance, which usually bites them in the ass (or would have bit them in the ass, if the standards for software weren't so low these days).