I propose the following grand challenge question for SBE 2020: can we develop a complete theory of human behavior that is predictive in all contexts? The motivation for this question is the fact that the different disciplines within SBE do have a common subject: Homo sapiens. Therefore, psychological, sociological, neuroscientific, and economic implications of human behavior should be mutually consistent. When they contradict each other - as they have in the context of financial decisions - this signals important learning opportunities. By confronting and attempting to reconcile inconsistencies across disciplines, we develop a more complete understanding of human behavior than any single discipline can provide. The National Science Foundation can foster this process of “consilience” in at least four ways: (1) issuing RFPs around aspects of human behavior, not around disciplines; (2) holding annual conferences where PI’s across NSF directorates present their latest research and their most challenging open questions; (3) organizing “summer camps” for NSF graduate fellowship recipients at the start of their graduate careers, where they are exposed to a broad array of research through introductory lectures by NSF PI’s; and (4) broadening the NSF grant review process to include referees from multiple disciplines.