My hopefully-better-expressed point is that it's easy to interpret the robustness principle in different ways, some of which lead to better code, and some of which... don't.
No worries. I think the philosophy is rooted in the fact that you can't control what other parties will send you; you can only control what you send in response. So that's the main thing to keep in mind.
It's sort of like the good life advice you hear occasionally: you can't control other peoples' actions; only your own. Emotional maturity, etc.
Isn't that missing the point of the robustness principle, which is more related to say, networking, and accepting things that aren't strictly to RFC spec, but when sending things, you match the spec to the letter?
My hopefully-better-expressed point is that it's easy to interpret the robustness principle in different ways, some of which lead to better code, and some of which... don't.