A bunch of people are looking at a train. Why is it moving? The superstitious peasant says it’s possessed by the devil. The uneducated guy next to him says it’s moving because the wheels are turning. Their friend, Captain Obvious, says that the smoke coming out of the engine is causing the movement.
Why are these explanations wrong? The first one can’t be proven or disproven, which makes it crazy, in Tolstoy's opinion. The second one is just a way of restating the question and just leads to another question – why are the wheels moving, then? And the third is just grabbing the first noticeable thing about the movement and making it the cause of the movement for no reason.
So yeah, bad calls all around.
This is just a long analogy for Tolstoy’s complaint about historians: all around him this is how historians are explaining events.