People adjust to changes in some economic conditions with a reasonable degree of predictability. When department stores announce lower prices, customers will pour through the doors. The lower the prices go, the larger the crowd will be. When the price of gasoline goes up, drivers will make fewer and shorter trips. If the price stays up, drivers will buy smaller, more economical cars. Even the Defense Department will reduce its planned purchases of tanks and bombers when their prices rise.

Behavior that is not measured in dollars and cents is also predictable in some respects. Students who stray from the sidewalks to dirt paths on sunny days stick to concrete when the weather is damp. Professors who raise their course requirements and grading standards find their classes shrinking in size. Small children shy away from doing things for which they recently have been punished.