It's Rules of Thumb, All the Way Down

My father was a door-to-door salesman of machine-generated literature, for the consumption of machines.

His biggest clients were dairy farmers with balky milking machines.

The theory at the time was that machines, when read to, would be more efficient and require less repair; just as houseplants, when spoken to, have greater well-being.

In fact, the benefits of literature have not been proven except in the case of machine literature, wherein studies have shown the recitation of such resulted in more even distribution of lubrication among working machine parts.

Why? We still don't know. As in all science, a relationship can only be proven to some extent, until it is overthrown.

There is no certainty, only the adoption of clever new heuristics, based on newly-proven weak relationships.

In other words, "It's Rules of Thumb, All the Way Down."