Fallacies: B (Part 3 of 3)

Core idea

The final B-entries gather science misconceptions that share a suspiciously clean shape — a round number, a memorable rule, a story too neat to question. The body renews itself "every seven years": there is no evidence for the figure, which was probably borrowed from the symbolism of seven. Water boils "at 212 degrees": true only for pure water at sea-level pressure. We use "ten percent of our brains": disproved by the brain's energy budget alone, since an organ that idle would not consume a fifth of the body's fuel.

The topic also runs through claims that sound mechanical but are not. A bull is enraged by red — no; bulls are colour-blind to red and react identically to a white cape, so the fury is the cape's movement and the spectacle around it. The Golden Gate Bridge is "perpetually repainted" — a touch-up legend borrowed from Scotland's Forth Bridge. The through-line: a fact gets repeated until its tidiness becomes its credential.

Why it matters

Neat numbers are sticky. "Seven years" and "ten percent" survive precisely because they are easy to remember and pleasant to say, not because anyone checked them. The book's value is in showing that memorability and truth are unrelated properties — a claim can be perfectly quotable and completely unfounded.

Some of these myths also do measurable harm. The belief that brain cells, once lost, are gone forever was used to scare people about ordinary acts, and was simply overturned when adult neurogenesis was confirmed. The "skin can't burn in cloudy weather" myth invites real sunburn, because ultraviolet passes through cloud. When a tidy rule is wrong, people make decisions on it — and the cost lands on their bodies, not on the rule.

Key takeaways

Mental model

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Practical application

The skill to practise here is treating roundness as a red flag. A claim built on exactly seven years, exactly ten percent, exactly 212 degrees is asking to be remembered, not believed. Ask: under what conditions does this hold, who measured it, and does the precise number have any source beyond repetition?

Example

A fitness post insists you "only burn fat after twenty minutes of cardio." Test it for tidiness. The round figure — twenty minutes — is the tell; real metabolism does not flip a switch on a clock. Ask for conditions: the body burns a mix of fat and carbohydrate continuously, and the proportion shifts gradually with intensity and duration, not at a threshold. Then trace the number: it descends from a simplified gym handout, much as "seven years" descended from the symbolism of seven. The honest version keeps the kernel — longer sessions do shift fuel use — but drops the magic minute. A precise number with no source behind it is decoration, not data.

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