Which is worth more: a container of water, or a container full of gold coins? I suspect that you’ll say the latter—the gold coins. Water is inexpensive or free, because there’s lots of it, and it’s easy to obtain, whereas gold is rare and more valuable to most people. But what we value can change with our context. For example, what if you were stranded in the desert without any water for two days, and you came across someone with a container of water. Well, you have no other ac- cess to water, and your life depends on getting it. In such circumstances, most people would gladly exchange all their gold for that container of water.