You are right, Susan. I have not met all the bears. They are "predictable as pie" in that the basic premise is to increase the distance between yourself and them, because they can kill you, even though they are unpredictable enough not to. "My understanding of bears" is of course going to differ with others' depending on unpredictable circumstances, thus the unpredictability of bears.

So again, unpredictable and yet as predictable as pie.

Or maybe you like 'predictably unpredictable' better.