The assumption that decision makers choose actions to maximize their preferences is a central tenet in economics. This assumption is often justied either formally or informally by appealing to evolutionary arguments. In contrast, we show that in almost every game and for almost every family of...

Players in a congestion game may differ from one another in their intrinsic preferences (e.g., the benefit they get from using a specific resource), their contribution to congestion, or both. In many cases of interest, intrinsic preferences and the negative effect of congestion are (additively...