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Where did our “Rules of Thumb” REALLY come from..?

The reason our brains love Micro-Scripts so much is because our brains our wired to use rules of thumb to deliver life-saving decisions in critical situations using the least amount of data. Not just human brains, all creatures’ brains have been pre-installed with these “in case of fire, break glass!” emergency instructions since dinosaur days. These rules are generally what’s operating when we feelĀ  “intuition.” Most of them are unconscious–that’s how an eight year old instinctively knows how to catch a baseball or dodge a snowball– because in the days when we were mostly prey, we had to be able to instantly judge (without doing a thousand differential equations) if the rock thrown was going to hit us in the head, or miss. The simple rule is: if the angle stays constant, duck!

So when we re-create this kind of ultra-compact decision making by making Micro-Scripts that are easy to remember, repeat, and store for quick use, our brains thank us for it–even when we’re not inĀ  mortal danger anymore (Pork is the other white meat. What would Jesus do? Where there’s smoke there’s fire). By the way, the fancy scientific word for rule of thumb is called a heuristic and the one above about “keep the angle constant” is called the “Gaze Heuristic.”

In fact, it turns out that the phrase “rule of thumb” is, well naturally, a rule of thumb. I am told that the rule pertained to the complex protocols and traditions in the Middle Ages about beating one’s wife. The rule of thumb was, you’re not supposed to beat your wife with any stick that’s wider than the width of your thumb. Back then, they must have thought that rule was quite the win/win. In a fit of drunken rage, any ogre husband could quickly pick out the perfect club, be certain he’d keep his wench in good working order after the beating, yet be confident throughout that the sheriff would not come and cut off his thumbs for a rules-of-beating-your-wife violation.

They were pretty good at coming up with Micro-Scripts in the Middle Ages, you’d have to say.

If you’re interested in heuristics and the rules of thumb that guide intuition, the best book on the subject is called Gut Feelings: The Intelligence of the Unconscious by Gerd Gigerenzer.

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