Comment by TheZenPsycho

I think the take away is not "do not optimise at all ever" it's about not just optimising your code, but optimise the time you spend optimising it. Do not spend 2 weeks micro-optimising a loop that, in reality, has no effect on the end user's experience, and ultimately makes the code base just much more difficult to maintain.

What you want to do is try to get most of your FINITE and EXPENSIVE development time on optimising things that actually matter to user experience.