When I think "premature optimization," I think of things like making a tradeoff in favor of performance without justification. It could be a sacrifice of readability by writing uglier but more optimized code that's difficult to understand, or spending time researching the optimal write pattern for a database that I could spend developing other things.

I don't think I should ignore what I already know and intentionally pessimize the first draft in the name of avoiding premature optimization.