While that&#x27;s true, it is often confused with the (wrong) assumption that: &quot;don&#x27;t try to do things efficiently; just measure later and redo the slow parts&quot;.<p>More often than not, if you don&#x27;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&#x27;s no specific culprit that&#x27;s making things so slow; at which point, you need to rewrite the whole thing.<p>Efficiency should be <i>considered</i> from the beginning in most projects, or later optimizations will be on the scale of &quot;massive undertaking&quot; to &quot;complete rewrite&quot;.