Donald Knuth famously opined:

“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.”

I broadly agree. It's incredibly difficult to guess which parts of our code will turn out to be performance bottlenecks, and, conversely, which parts will become development bottlenecks because of the obscurity introduced by manual optimization. Eventually one develops instincts for this sort of thing, though they may be of less general applicability than we think …

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