Startup founders, aspiring filmmakers, and would-be worldsavers “have to” be enthusiastic and positive. They have to sell their models—to skeptical investors, to potential hires, and oddly often to themselves—and many people struggle to hold both determined confidence and fundamental uncertainty in their minds at the same time. Instead, their brains use mood to encourage them to alternate. The euphoric half of the cycle is where assumptions are taken to their conclusion—where you collide your models with reality by building code, attempting to enroll customers, and so on. And the despair half is where those assumptions are challenged and questioned—where all of the fears and doubts and worrying bits of evidence that you’ve been holding off on looking at are allowed to come forward.