It's interesting to contrast "Measure. Don't tune for speed until you've measured" with Jeff Dean's "Latency Numbers Every Programmer Should Know" [0].
Dean is saying (implicitly) that you can estimate performance, and therefore you can design for speed a priori - without measuring, and, indeed, before there is anything to measure.
I suspect that both authors would agree that there's a happy medium: you absolutely can and should use your knowledge to design for speed, but given an implementation of a reasonable design, you need measurement to "tune" or improve incrementally.
Dean is saying (implicitly) that you can estimate performance, and therefore you can design for speed a priori - without measuring, and, indeed, before there is anything to measure.
I suspect that both authors would agree that there's a happy medium: you absolutely can and should use your knowledge to design for speed, but given an implementation of a reasonable design, you need measurement to "tune" or improve incrementally.
0: https://gist.github.com/jboner/2841832