I love fables, aphorisms, proverbs, paradoxes, and koans—and anything that makes a good teaching story.

Sometimes, a joke makes a good teaching story. When I’m talking to people, or myself, I often find myself invoking an old joke to make a particular point.

Here’s my version of this joke:

In the dark hours of the very early morning, a policeman was walking around a neighborhood to check on things. He came across a man who had clearly had too much to drink. With uneven steps, the guy was walking around in circles under a streetlight, with his head bent down to look at the ground.

The policeman walked up and said, “What’s the trouble here? Do you need any help?”

The man replied, “I lost my wallet.”

The policeman said, “Oh, no. I’ll help you look.” They search together for a few minutes, then the policeman asked, “Are you sure you dropped it around here?”

The man said, “Oh, no, I lost it over there, in the park, but the light is better here.”

There’s a kind of observational bias that takes its name from this joke: it’s called the “streetlight effect.” It describes the fact that sometimes we look for something only where it’s easy to search.

I experienced this effect myself, recently. As part of the work for my new book Life in Five Senses, I created a quiz, the “What’s Your Neglected Sense?” quiz. (If I do say so myself, this quick, free quiz is extremely useful and super fun.)

Once the quiz was finished, of course, I wanted to spread the word. I wanted to tell as many people as possible about the quiz.

But what I found was that I kept thinking of more and more ways to communicate with the people I was already in touch with. I wasn’t spending any time thinking about ways to reach people who had no connection to me.

To put it a different way, I found it easier to look on the brightly lit ground beneath the lamppost rather than to search in the shadowy park—even though that’s where I’d find the outcome I sought.

If you want to take the quiz, you can find it at gretchenrubin.com/quiz.