I am not convinced about this. I can't really know what you mean based on this one sentence (or the parent comment from that one sentence), but the really good

I am not convinced about this. I can't really know what you mean based on this one sentence (or the parent comment from that one sentence), but the really good artists I know absolutely lay down rules for themselves. All art, fundamentally, emerges in part from creative constraints and from practice of communicating within them. And good artists absolutely know this (whether they would express it in this generalised way or not). Good artists can switch from medium to medium by exploring the constraints (beyond just the physical limits of charcoal or clay or stacking stones) and then figuring out how to communicate with them. But you don't really get very far without imposing additional restrictions on the work that help frame the message you're trying to convey. Artists who invent new mediums of expression do this same thing implicitly; the medium at some level is its constraints. So experienced artists usually do make up rules for themselves (or at least positive schemes and negative no-go areas) whether they write them down or not.