And then you quickly reach the conclusion that the only way to assess whether one of the implementation choices will be faster/less memory consuming/etc. in pro

And then you quickly reach the conclusion that the only way to assess whether one of the implementation choices will be faster/less memory consuming/etc. in production is to implement both, deploy to production and observe the performance on the actual workloads. And the findings don't generalize, so you can't actually learn from them and build a predictive theory. And this conclusion doesn't sit well with quite a number of developers, myself included, because I personally would like to be able to do the "right" choice without the brute force of "try everything and see what works better".