为了简单地模拟人类如何使这成为可能，我们需要一个基本的行为假设。假设人们试图尽可能地为自己做 – 或者，在他们的资源限制的情况下，根据他们的偏好最大化结果。换句话说，人们倾向于根据自己的最佳利益做出决定。经济学家说，这样做的人表现出理性行为。对个人的利益可以具有货币价值或情感价值。这种假设并不一定意味着人们做出了完美的决定。人们可能会受到他们所拥有的信息量的限制（例如，“当时这似乎是一个好主意！”）。同样，在这种情况下，“理性行为”并未说明人们偏好的质量或性质（“但我喜欢用锤子击打自己的头部！”）。偏好和约束之间的斗争意味着经济学家必须从根本上解决权衡问题。为了获得某些东西，我们必须耗尽我们的一些资源。换句话说，个人必须选择对他们最有价值的东西。例如，放弃20美元从Amazon.com购买新畅销书的人正在做出选择。这本书比20美元更有价值。对于不一定具有货币价值的事物做出相同的选择。放弃三小时的时间在电视上观看职业棒球比赛的人也在做出选择。观看比赛的满意度比观看比赛的时间更有价值。
In order to simply simulate how humans make this possible, we need a basic behavioral assumption. Suppose people try to do as much as they can – or, in the case of their resource constraints, maximize results based on their preferences. In other words, people tend to make decisions based on their best interests. Economists say that people who do this show rational behavior. The individual’s interests can have monetary or emotional value. This assumption does not necessarily mean that people make the perfect decision. People may be limited by the amount of information they have (for example, “this seems like a good idea at the time!”). Similarly, in this case, “rational behavior” does not indicate the quality or nature of people’s preferences (“but I like to hit my head with a hammer!”). The struggle between preferences and constraints means that economists must fundamentally resolve trade-offs. In order to get something, we must exhaust some of our resources. In other words, individuals must choose what is most valuable to them. For example, those who give up $20 to buy a new bestseller from Amazon.com are making choices. This book is more valuable than $20. Make the same choice for things that don’t necessarily have a monetary value. Those who give up three hours of watching professional baseball games on TV are also making choices. Satisfaction with watching the game is more valuable than watching the game.