<p>It is estimated that five hundred billion dollars are spent on philanthropy every year. How should we spend those resources to do the most good? One possible answer, based on expected-value reasoning, is that we should spend those resources “fanatically” on interventions that can possibly produce enormous benefit, but with minuscule chance of success. This paper develops a new kind of knowledge-first decision theory that implies that we should not spend those resources fanatically. As such, this paper would be of interest to anyone who wants to explore a fresh reason against acting fanatically, and it would be of interest to anyone looking for a template on how to develop a knowledge-first decision theory of their own.</p>