"to identify which components of what you are building _must_ be perfect"

Well, but by the words of your former CEO (and my opinion) those parts would then have infinite costs, too... if they really need to be perfect. I mean, it is awesome, when you do a big feature change and it all just runs smooth without problems, because your design was well thought out, but you cannot think of every future change to come - and when you still try, chances are you get stuck and waste your time and risk the flow of the whole project. I rather tend to think about the current needs first and the immediate future second, but everything after that, I spend not much thought anymore.