Over the past decade, governments and institutions the world over have spent roughly $9 billion annually to combat public health scourges such as HIV/AIDS, malaria, and waterborne illnesses. Yet more than 13 million people die each year, mostly in developing countries, from medical conditions for which effective prevention or treatment exists. Why?

The common response is to point to the barriers to health care created by its cost and uneven availability. To be sure, the challenges of large-scale coordination and logistics do play a role, particularly in countries with poor infrastructure and governance. But improving access to—and the use of—essential health products and services will take more than addressing proximity and price.

My lab and field research in Africa, Latin America, and Southeast Asia, and that of other development and behavioral economists around the world, points to another key factor in the health care equation: human nature. Behavioral economics has shown us that we don’t always act in our own best interests, no matter where we live. This is as true of health decisions as it is of economic ones. An array of biases, limits on cognition, and motivations leads people from all walks of life to make suboptimal health choices.

The good news, as this article will show, is that human nature can also be a source of solutions. By understanding the cognitive processes underlying our health choices and applying the tools of behavioral economics, it’s possible to design products and programs that encourage good health decisions and long-term behavior change.