While that's true, it is often confused with the (wrong) assumption that: "don't try to do things efficiently; just measure later and redo the slow parts". Mor

While that's true, it is often confused with the (wrong) assumption that: "don't try to do things efficiently; just measure later and redo the slow parts". More often than not, if you don't think about performance characteristics beforehand, then -- after taking care of the low hanging fruit -- you find out that time is wasted all over, and there's no specific culprit that's making things so slow; at which point, you need to rewrite the whole thing. Efficiency should be considered from the beginning in most projects, or later optimizations will be on the scale of "massive undertaking" to "complete rewrite".