When is optimisation premature?

Question

As Knuth said,

We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil.

Answer 1

The need to use a profiler should be left for extreme cases. The engineers of the project should be aware of where performance bottlenecks are.

I think "premature optimisation" is incredibly subjective.

If I am writing some code and I know that I should be using a Hashtable then I will do that. I won't implement it in some flawed way and then wait for the bug report to arrive a month or a year later when somebody is having a problem with it.

Redesign is more costly than optimising a design in obvious ways from the start.

Obviously some small things will be missed the first time around but these are rarely key design decisions.

Therefore: NOT optimising a design is IMO a code smell in and of itself.