We often make our everyday decisions on the basis of thought patterns that, unfortunately, are always wrong – but only under certain circumstances. These thinking patterns also have a strong influence on the way we do science. And because errors can teach us a great deal about how systems work in general, and about how we think in particular, it is worth taking a closer look at them.

Today I want to introduce you to a particularly perplexing pattern of thinking: similarity thinking.
Similarity thinking is the basic assumption that cause and effect are similar. This means that large, small or complex events can be reasonably reliably attributed to correspondingly large, small or complex causes. This way of thinking is mostly useful because this is often the case (emphasis on “often”).

Here are a few nice examples of what it looks like when this way of thinking gets it wrong:

  • Turmeric is said to be good against yellow fever precisely because of its yellow colour.
  • According to the Fang Indians, eating squirrels promotes pregnancy because squirrels come out of holes.
  • Among the Hopi, on the other hand, it is taboo for pregnant women to eat squirrels because they hatch in holes.
  • And among a tribe in Hawaii, all baskets and other closed objects must be opened during childbirth. (Examples taken from Klix, F. (1993): Awakening Thinking: Mental Performance from an Evolutionary Psychological Perspective).

Sounds rather ridiculous to us, but we enlightened Central Europeans are no better:
Some 77% of Germans regularly read horoscopes that talk of stubborn Capricorns, courageous Lions and balanced Librans. But as Douglas Adams put it so well: Why should lumps of rock floating around in space know more about my life than I do?
And anyone who has ever thrown the dice for high numbers with particular verve will have similar thoughts…