For PC, Norm need to be changed often, it's like changing passwords often.

http://tomwoods.com/podcast/ep-726-how-and-why-progressives-...

There is thought that changing your password often might make passwords worse... Don't have a citation at the moment (phone) but, the tl;dr is that often changing means you're more likely to pick smaller passwords that are easier to construct, and to remember, making them weaker than something you'll commit to for a longer time.

So... maybe not the best analogy, but understood.