I believe it's almost backwards: with IA, you get small mistakes accumulating into irreversible changes (with all sorts of temptations to declare the result "good enough"), while with FAI you have a chance of getting it absolutely right at some point. The process of designing FAI doesn't involve any abrupt change, the same way as you'd expect for IA. On the other hand, if there is no point with IA where you can "let go" and be sure the result holds the required preference, the "abrupt change" of deploying FAI is the point where you actually win.