Chabad chassidic teaching discusses two levels of knowledge: “positive knowledge” and “negative knowledge.” Positive knowledge is when you understand something; negative knowledge is when there is something beyond your comprehension, and you understand what it is that you do not understand. Negative knowledge is higher than positive knowledge, since the most difficult thing for the human mind to comprehend is its own limits. But higher yet, say the chassidic masters, is a third level: understanding that there are truths that are beyond the domain of “negative knowledge” as well; comprehending that you cannot even comprehend what it is that you do not comprehend. Chassidim would illustrate this with the following parable:

The story is told of a group of coachmen in a small town in the backwoods of Russia who heard some disturbing news from the big city. Frightening things were happening in the world: bands of iron were being laid across the plains and forests of Russia, upon which an iron monster, who ate coal and spewed fire and smoke, would move three times faster than the fleetest team of horses. It was said that this demon could pull a hundred iron coaches and thousands of passengers. No longer would anyone need to hire a coach and coachman to go from town to town. No longer will merchants negotiate the price of a wagon to take their wares to the market in Leipzig. People were already travelling from Moscow to Petersburg in this manner, and soon these roads of iron will connect every town in Russia.

“And how many horses does this machine use?” asked Misha, the oldest and ablest of the coachmen. “None whatsoever,” said Grisha, who was the source of the news. “That’s the whole point: no horses, and no coachmen.” “Impossible,” said Misha with authority. “A hundred iron coaches, no horses? Impossible!”

“But here’s the letter from my cousin from Smolensk. He writes that the iron rails have already reached the city, and that next month the first of these machines will arrive from Moscow.” After much debate, the coachmen decided to travel to the city and see for themselves.

At the appointed time, they stood at the edge of the crowd that had gathered on the platform at the newly erected station. They heard it before they saw it, an unearthly sound of crashing metal and a thousand charging bulls. And then, in a huge cloud of black smoke, it appeared: a line of iron coaches stretching as far as the eye could see, traveling faster than the mightiest horse, a shrieking iron monster at their head. It pulled up alongside the cheering crowd, let go a final ear-piercing wail, and died.

As the crowd surged towards the train, the coachmen remained rooted to the ground, mouths agape, stunned to the very core of their souls. Misha was the first to recover. Ignoring the train of carriages and their disembarking passengers, he boldly approached the engine. Carefully he circled the still shuddering monster, running his eyes over every inch of its surface. He peered into the engineer’s cabin and crouched between the wheels to examine the undercarriage. Muttering to himself, he rejoined his fellow coachmen on the platform.

“Amazing!” he kept saying to himself. “What a horse! What a horse!”

“A horse?” asked his colleagues.

“Of course,” said the veteran coachman. “There’s got to be a horse hidden somewhere in there. Think of it—a horse, probably no bigger than a kitten, who can pull one hundred iron coaches. What a horse!”