Tracing the Cause Backwards

I really liked the section in the book about tracing the cause backwards. The book goes through a convoluted set of events to trace the cause of Dick waking up, but after it goes through everything, it says "but really... This is silly. We could go backwards forever. We stop at the first step: Spot's barking caused Dick to wake up. We stop because as we trace the cause back further it becomes too hard to fill in the normal conditions." So basically, it's too hard to figure what started this chain of events, so we just go with the one most directly connected to Dick waking up. Dick woke up because Spot barked. I thought this was great because when I read it, I phrased it in my mind as "You know what? screw it. Let's just blame Spot." So it turns out after all this time that I wasn't doing this because I was lazy, it turns out that it's okay to do this because it's just too hard.