Two people go into a restaurant. The waiter takes their orders, then brings a basket of rolls. There are three rolls for two people. This forces one of them at some point to awkwardly ask the other, in as unselfish a voice as possible, “Are you gonna eat that last roll?”

Sure, the customers could ask for more rolls, but that request still comes after the first three are consumed. Why not fill the basket with four rolls, easily divisible by an even number of people?

Of course they’ll bring a basket of four — as soon as three people sit down.