How much would it take for us to have enough money? Remarkably, studies show that most people, regardless of income, answer the question the same way: We need about 10% more to feel comfortable. Ten percent will make a difference, and whether we earn $30,000 per year or $60,000 or $250,000 or a cool million, just 10% more is what we want.

When people are asked the same question over time, Loyola Marymount University Professor Christopher Kaczor reports "when they do get that 10%, which typically happens over the course of a few years, they want just another 10%, and so on, ad infinitum." This reality prompted British psychoanalyst Joan Riviere to make the following observation: "by its very nature [greed] is endless and never assuaged; and by being a form of the impulse to live, it ceases only with death."