I love a good teaching story. I also love any story that illuminates some deep aspect of human nature.

Every once in a while, I hear or read a story about something a person said or did, and some bell goes off in my head. I think, “Wow, there’s some deep principle at work here, there’s some profound lesson, but I can’t yet grasp it.”

That happened to me with the Four Tendencies. Creating my Four Tendencies personality framework is one of the most difficult challenges of my intellectual life, and it’s one of the things I’m most proud of.

During an ordinary lunch with a friend, she said offhandedly, “I want to get myself in the habit of running, but I can’t, and it really bothers me.” Then she added, almost as an aside, “When I was on the high school track team, I never missed track practice, so why can’t I go running now?”

“Why?” I echoed.

“Well, it’s so hard to make time for ourselves.”

“Hmmm,” I said. “Actually, I don’t have any trouble making time for myself.”

Even after we’d said good-bye, I couldn’t stop thinking about our exchange. She was the same person, aiming to do the same activity. She’d been able to go running in the past, but not now. Why? Was it her age, her motivation, her family situation, the location, team spirit, or something else? Also, why could I make time for myself, but she couldn’t?

For months, I puzzled over these questions—until finally, I had my eureka moment. The key question is: “How do you respond to expectations?”

When you know the answer, you know whether you’re an Upholder, Questioner, Obliger, or Rebel—the four types in my Four Tendencies framework. You can take my quiz here to find your tendency.

There’s another story I heard—one that I’ve never forgotten.

I was on my book tour for my book Happier at Home, and at one stop, I had dinner with some very nice publishing people, and one of them told me this story. She’d always been terribly afraid of flying—dreaded it, had white knuckles the whole time she was in the air, hated to fly. But sometimes she did make herself get on an airplane.

Then one weekend came she had to fly to a friend’s wedding. She made the trip, she had a great time, but she had to fly home very early on the morning after the wedding. The night of the wedding, she’d gotten so drunk that the next morning, she was still drunk, plus she had a headache, was dizzy, and felt extremely sick. She felt terrible and threw up in the airport and also on the plane during the flight.

But here’s what’s interesting.

She told me, “For the first time, I wasn’t scared of flying. I was so sick that my body just couldn’t produce any kind of fear response. I couldn’t think about anything other than how awful I felt. And since that morning, I’ve never been afraid to fly.”

I think this story holds many lessons about emotions, fear, and the connection between the body and mind. It suggests possible new avenues of treating anxiety. I haven’t yet fully worked it out, the way that I worked out the Four Tendencies, but I keep it in mind.