In their classic Your Money or Your Life, Joe Dominguez and Vicki Robin argue that the relationship between spending and happiness is non-linear. More spending brings more fulfillment — up to a point. But spending too much can actually have a negative impact on your quality of life. The authors suggest that personal fulfillment — that is, contentment — can be graphed on a curve that looks like this: Beyond the peak, Stuff starts to take control of your life.