Let's Take A Closer Look

Explaining complicated subject matter simply since 1986

Our eyes tell us the top horizontal line is quite obviously longer than the bottom horizontal line. This famous example of an optical illusion purposely deceives us by tricking our eyes into seeing what isn’t there. Illusion is of course the principle behind what little kids like to call magic. Adults know it as sleight of hand and the old mumbo-jumbo. It is the placement of the arrows that tricks our eyes.

What happens when we override our impressions and test which is longer?

Let’s grab a ruler and measure both lines. Unless we have a really weird ruler, we find they are the exact same length. But even after we know for certain they are equal, we still “see” the top line as longer. Why? Because our brains process and capture visual clues rapidly and unconsciously. To avoid falling victim to illusions, we can try something quite simple.

Yes, we can learn to mistrust our initial impressions

To do that, we must be able to:

  1. Recognize an illusion.
  2. Recall what we know about it.
  3. Use our brains to override our eyeballs.

When we learn how to do these three things, we will still see the top line as longer than the bottom line, but we will never again be tricked by the Müller-Lyer illusion.

What do optical illusions have to do with the price of tea in China?

Not all illusions are visual. There are illusions of thought, called cognitive illusions.

How many animals of each kind did Moses take on the Ark?

Most people say two, even when they know it was Noah, not Moses. When words in a sentence or question are replaced with similar but incorrect terms, people have difficulty detecting the misrepresentations. This tendency to overlook distortions is called the Moses Illusion. We fall victim to the Moses illusion because we don’t process every word deeply. Usually we just skim over the words, especially those we assume we already know. Nobel-winning psychologist Daniel Kahneman says “When faced with a difficult question, we often answer an easier one instead, usually without noticing the substitution.”

The question I hear most often about cognitive illusions is whether they can be overcome when the stakes are high

The answer is yes, but only when we have learned to recognize situations where deceptions are likely and ask our most powerful tool – our brain – for help.

Let’s try another

  • A bat and a ball cost $1.10.
  • The bat costs one dollar more than the ball.
  • How much does the ball cost? 

If you said ten cents, you are an intuitive thinker who trusted your instincts

If you said five cents, you are someone who solves problems analytically. Analytical problem-solvers figured it out before answering, so they can skip the next section.

Intuitive thinkers, try this

If the ball costs $ .10 as you say, and the bat costs one dollar more than the ball, then the bat has to cost $1.10, which means the bat and the ball together have to cost $1.20, which means the ball does not cost ten cents, which means your adding machine is as wacky as your ruler.

Analytical types work it out in a few seconds:

 Bat $1.05 + ball $.05 = $1.10


The cost of learning to avoid cognitive illusions has enormous value to people whose jobs require them to use data. It’s one of the ways I help people learn to avoid misinformation traps.

Want to look at old things in new ways and see the commonplace in more detail?

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