Why experts miss the easy answer

Experience makes people faster. Sometimes it also makes them blind.

Here is a puzzle from the early 1940s.

You have three water jars. Jar A holds 21 cups. Jar B holds 127. Jar C holds 3. Using only these jars, measure out exactly 100 cups.

The answer: fill B, pour from it to fill A once, then fill C twice. 127 minus 21 minus 3 minus 3 leaves 100.

Now do a few more with different numbers. The same method works every time. B, minus A, minus C twice.

Then comes this one. Jar A holds 23. Jar B holds 49. Jar C holds 3. Measure exactly 20.

Most people reach for the method they just learned. 49 minus 23 minus 3 minus 3. It works.

What most do not notice is that A minus C also works. 23 minus 3. One step instead of four.

The psychologist Abraham Luchins ran this experiment and published it in 1942. People who had practiced the long method tended to keep using it, even with the short one in plain view. Given a later problem where only the short method worked, many got stuck entirely. People who never practiced the long method found the simple answer easily.

Luchins called it the Einstellung effect, from a German word for a setting, or a mental set.

It would be comforting to think this only happens to beginners.

It happens to experts too.

In 2008, researchers Merim Bilalić, Peter McLeod, and Fernand Gobet showed strong chess players positions with two solutions: a familiar pattern that won in five moves, and a less familiar one that won in three. Many of the experts found only the familiar one.

Then the researchers tracked their eyes. The players said they were searching for something better. Their eyes kept drifting back to the squares of the solution they already knew.

The first idea did more than come to mind first. It quietly steered the whole search.

Experience is mostly a gift. It is why a veteran nurse spots trouble a new one misses, and why a seasoned editor can fix a paragraph in seconds.

But the same patterns that make experts fast can make them predictable. Knowing one good answer can hide a better one. The more often a method has worked, the harder it becomes to look past it.

Every mind does this. It is how minds save effort.

So what loosens the grip?

A few things seem to help. Stepping away before looking again. Explaining the problem to someone outside the field. Asking a blunt question: if the usual method were off the table, what then? And rereading old notes from before you knew so much, when more of the answers still seemed possible.

Expertise is worth building. It is also worth questioning, especially at the moment it feels most certain.

"I suppose it is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail."

Abraham Maslow, The Psychology of Science, 1966