"By the time a bartender knows what drink a man will have before he orders, there is little else about him worth knowing"

This quote by Don Marquis suggests that a bartender's ability to predict a client's drink order is a sign of their keen observation skills. It indicates that as soon as a bartender has actually determined what a customer will order, there is not much else to find out about them. This might be analyzed as a commentary on the shallow nature of human interaction. It recommends that individuals frequently don't put in the time to be familiar with each other on a deeper level, and instead rely on surface-level observations to make assumptions about one another. Marquis' quote could also be seen as a pointer to put in the time to learn more about individuals beyond their beverage order.