Unable to see outside, all he could know of the world beyond his prison was what he was able to deduce from the shadows that were projected on the wall by whatever passed by. Plato was talking about how we all are prisoners of our own bodies and know only what our senses tell us of the world beyond. We are still imprisoned in our own bodies, of course, and presumably always will be. But in the modern world we all are chained in caves of another kind as well, caves where the shadows on the walls are what we call statistics.
Statistics are both ancient and astonishingly modern.
When the shepherds of Plato's Attica counted their flocks, they were, of course, making a statistical analysis. But the word itself entered the English language only in 1787. It is no coincidence that that was also the decade James Watt patented the rotary steam engine. As the factory system, which had evolved in the middle of the eighteenth century, and the new power source spread, enterprises could operate on a far larger scale. The owner of a business that employs hundreds or thousands of people needs statistics.