I liked this footnote. A simple, intuitive explanation.

> If you pay $1.00 to press a button, and pressing the button pays you $0.99, you > will press the button zero times. If you get $1.01 instead, you will press the > button all the time.

One thought: If it only gives you $0.01 profit you'll (have to) push it more than if it gave you $1000 profit. There's a saturation point.