You were also looking for an example. Someone please correct me if I'm wrong.I stab you in the leg. You go to the hospital for treatment, where you slip on a puddle, hit your head on the floor, and die due to brain damage caused in the fall. Though this passes the "cause in fact" but-for test, but for my stabbing you never would have slipped in the hospital, it doesn't pass the proximate cause test. You slipping and falling in the hospital wasn't at all forseeable and I can't be held responsible for it.
Thanks for the great example. So, in your example, house "A" burning is a "cause in fact" of all of the other houses that burned, but it may only be treated as a proximate cause of house "B" burning?