How do you ever know that there aren't spots that can't be considerably improved? Does it matter that much? Any inefficiency apparently wasn't bad enough to sto

How do you ever know that there aren't spots that can't be considerably improved? Does it matter that much? Any inefficiency apparently wasn't bad enough to stop it being shipped. I actually struggle more with not treating every problem like some algorithmic puzzle to be solved in one pass with O(1) extra memory and just writing stupid, slow, straight-forward code.