You forgot the whole quote. "Programmers waste enormous amounts of time thinking about, or worrying about, the speed of noncritical parts of their programs, and

You forgot the whole quote. "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%." Knuth is saying that in most cases optimizing prematurely is not worth it, which is right, but just as critical is the part saying that there are parts where pays off to consider optimization early. Writing your logging function in assembly likely fits into the 97%. Writing your N-queens solver, if you're aiming for all-out speed, likely fits into the 3%. Of course not thinking about optimization at all will lead you down a path where your software is unoptimizable, or at least very difficult to optimize. Ask anyone who's had to optimize a video game that manages all objects in a scene graph, where reorganizing a cache hostile tangled web of pointers to base classes is a herculean feat.