In the days before inexpensive wristwatches, most people did not carry their own timepieces. Many towns built clock towers to help their citizens keep track of time. The towns paid for the clock towers with voluntary contributions from citizens. One town in the northeastern United States built a four-sided tower but put clock faces on only three sides of the tower. To most people, this seems bizarre. If you build a clock tower, why not put clock faces on all four sides? It turns out that one of the towns wealthy citizens refused to contribute money to help build the clock tower. The town officials decided not to put a clock face on the side of the tower facing this citizens house. In other words, the citizen tried unsuccessfully to get a free ride. The problem is that other citizens on the same side of town also suffered from not having a clock. In this case, preventing a free ride by one citizen caused problems for other citizens. It also caused inefficiency because the cost of a fourth clock was presumably much less than the foregone benefits to the excluded citizens.