But if you take the principle seriously, you don't have any basis upon which to reject the universal principle once you have established one. You're simply agreeing with me: don't actually have a universal principle. Just see how things go, and if they feel too wrong, change stuff. Yes, yes, try organizing around a "universal principle", but we know all along that this isn't actually what is guiding our evaluations. It's a simplification that we're trying out but the true principle(s) are unstated, and those are what we ultimately use to determine whether our stated principle was good.