We go beyond estimation of treatment effects of education and psychological skills on longevity by uncovering the mechanisms behind these effects. We decompose each treatment effect with respect to observed and unobserved mediators. The mediators are health behaviors, lifestyles, and earnings. We estimate the contribution of each observed mediator and the joint contribution of all unobserved mediators. We find a number of major mediators such as smoking tobacco, binge drinking of alcohol, doing physical exercise, unhealthy diet, marriage, and income. We also find that different skills act through different mediators, and that effects through mediators may cancel each other. (Coauthors Kai Hong, Kegon Tan.)