Here, for instance, is an improvised exchange between two actors in a class that Johnstone was teaching:

A: I’m having trouble with my leg.

B: I’m afraid I’ll have to amputate.

A: You can’t do that, Doctor.

B: Why not?

A: Because I’m rather attached to it.

B: (Losing heart) Come on, man.

A: I’ve got this growth on my arm too, Doctor.

The two actors involved in this scene quickly became very frustrated. They couldn’t keep the scene going. Actor A had made a joke—and a rather clever one (“I’m rather attached to it”)—but the scene itself wasn’t funny. So Johnstone stopped them and pointed out the problem. Actor A had violated the rule of agreement. His partner had made a suggestion, and he had turned it down. He had said, “You can’t do that, Doctor.” So the two started again, only this time with a renewed commitment to agreeing:

A: Augh!

B: Whatever is it, man?

A: It’s my leg, Doctor.

B: This looks nasty. I shall have to amputate.

A: It’s the one you amputated last time, Doctor.

B: You mean you’ve got a pain in your wooden leg?

A: Yes, Doctor.

B: You know what this means?

A: Not woodworm, Doctor!

B: Yes. We’ll have to remove it before it spreads to the rest of you.

(A’s chair collapses.)

B: My God! It’s spreading to the furniture!

Here are the same two people, with the same level of skill, playing exactly the same roles, and beginning almost exactly the same way. However, in the first case, the scene comes to a premature end, and in the second case, the scene is full of possibility. By following a simple rule, A and B became funny. “Good improvisers seem telepathic; everything looks pre-arranged,” Johnstone writes. “This is because they accept all offers made—which is something no ‘normal’ person would do.”

Here’s one more example, from a workshop conducted by Del Close, another of the fathers of improv. One actor is playing a police officer, the other a robber he’s chasing.

Cop: (Panting) Hey—I’m 50 years old and a little overweight. Can we stop and rest for a minute?

Robber: (Panting) You’re not gonna grab me if we rest?

Cop: Promise. Just for a few seconds—on the count of three. One, Two, Three.

Do you have to be particularly quick-witted or clever or light on your feet to play that scene? Not really. It’s a perfectly straightforward conversation. The humor arises entirely out of how steadfastly the participants adhere to the rule that no suggestion can be denied. If you can create the right framework, all of a sudden, engaging in the kind of fluid, effortless, spur-of-the-moment dialogue that makes for good improv theater becomes a lot easier. This is what Paul Van Riper understood in Millennium Challenge. He didn’t just put his team up onstage and hope and pray that funny dialogue popped into their heads. He created the conditions for successful spontaneity.

On Paul Van Riper’s first tour in Southeast Asia, when he was out in the bush, serving as an advisor to the South Vietnamese, he would often hear gunfire in the distance. He was then a young lieutenant new to combat, and his first thought was always to get on the radio and ask the troops in the field what was happening. After several weeks of this, however, he realized that the people he was calling on the radio had no more idea than he did about what the gunfire meant. It was just gunfire. It was the beginning of something—but what that something was was not yet clear. So Van Riper stopped asking. On his second tour of Vietnam, whenever he heard gunfire, he would wait. “I would look at my watch,” Van Riper says, “and the reason I looked was that I wasn’t going to do a thing for five minutes. If they needed help, they were going to holler. And after five minutes, if things had settled down, I still wouldn’t do anything. You’ve got to let people work out the situation and work out what’s happening. The danger in calling is that they’ll tell you anything to get you off their backs, and if you act on that and take it at face value, you could make a mistake. Plus you are diverting them. Now they are looking upward instead of downward. You’re preventing them from resolving the situation.”

Van Riper carried this lesson with him when he took over the helm of Red Team. “The first thing I told our staff is that we would be in command and out of control,” Van Riper says, echoing the words of the management guru Kevin Kelly. “By that, I mean that the overall guidance and the intent were provided by me and the senior leadership, but the forces in the field wouldn’t depend on intricate orders coming from the top. They were to use their own initiative and be innovative as they went forward. Almost every day, the commander of the Red air forces came up with different ideas of how he was going to pull this together, using these general techniques of trying to overwhelm Blue Team from different directions. But he never got specific guidance from me of how to do it. Just the intent.”

Once the fighting started, Van Riper didn’t want introspection. He didn’t want long meetings. He didn’t want explanations. “I told our staff that we would use none of the terminology that Blue Team was using. I never wanted to hear that word ‘effects,’ except in a normal conversation. I didn’t want to hear about Operational Net Assessment. We would not get caught up in any of these mechanistic processes. We would use the wisdom, the experience, and the good judgment of the people we had.”

This kind of management system clearly has its risks. It meant Van Riper didn’t always have a clear idea of what his troops were up to. It meant he had to place a lot of trust in his subordinates. It was, by his own admission, a “messy” way to make decisions. But it had one overwhelming advantage: allowing people to operate without having to explain themselves constantly turns out to be like the rule of agreement in improv. It enables rapid cognition.

Let me give you a very simple example of this. Picture, in your mind, the face of the waiter or waitress who served you the last time you ate at a restaurant, or the person who sat next to you on the bus today. Any stranger whom you’ve seen recently will do. Now, if I were to ask you to pick that person out of a police lineup, could you do it? I suspect you could. Recognizing someone’s face is a classic example of unconscious cognition. We don’t have to think about it. Faces just pop into our minds. But suppose I were to ask you to take a pen and paper and write down in as much detail as you can what your person looks like. Describe her face. What color was her hair? What was she wearing? Was she wearing any jewelry? Believe it or not, you will now do a lot worse at picking that face out of a lineup. This is because the act of describing a face has the effect of impairing your otherwise effortless ability to subsequently recognize that face.

The psychologist Jonathan W. Schooler, who pioneered research on this effect, calls it verbal overshadowing. Your brain has a part (the left hemisphere) that thinks in words, and a part (the right hemisphere) that thinks in pictures, and what happened when you described the face in words was that your actual visual memory was displaced. Your thinking was bumped from the right to the left hemisphere. When you were faced with the lineup the second time around, what you were drawing on was your memory of what you said the waitress looked like, not your memory of what you saw she looked like. And that’s a problem because when it comes to faces, we are an awful lot better at visual recognition than we are at verbal description. If I were to show you a picture of Marilyn Monroe or Albert Einstein, you’d recognize both faces in a fraction of a second. My guess is that right now you can “see” them both almost perfectly in your imagination. But how accurately can you describe them? If you wrote a paragraph on Marilyn Monroe’s face, without telling me whom you were writing about, could I guess who it was? We all have an instinctive memory for faces. But by forcing you to verbalize that memory—to explain yourself—I separate you from those instincts.