Why is P(Doom) such a bad argument?

Imagine a patient diagnosed with a life-threatening illness who is given a ten percent chance of survival. Medical research shows that patients who maintain an unshakeable belief in their recovery actually experience better immune function and higher survival rates. The evidence for their full recovery is weak, but the consequences of believing in it are life-saving. In a case like this, insisting on cold, hard evidence isn't just stubborn; it is dangerous. Choosing what to believe based on outcome rather than raw evidence is not foolish. It is a powerful, rational strategy known in philosophy as **pragmatism**—the idea that the truth or value of an idea lies in its practical consequences. ## The Pragmatic Leap We often assume that rationality means acting like a courtroom judge, weighing evidence before adopting a belief. But in the real world, human beings must act, often with incomplete information. The American philosopher and psychologist [William James](https://en.wikipedia.org/wiki/William_James) famously championed this approach in his landmark 1896 essay, [*The Will to Believe*](https://en.wikipedia.org/wiki/The_Will_to_Believe). James argued that when we face a decision that is momentous, forced, and cannot be decided by intellectual evidence, we have every right to let our heart and expectations guide us. > "Our passional nature not only lawfully may, but must, decide an option between propositions, whenever it is a genuine option that cannot by its nature be decided on intellectual grounds." James pointed out that waiting for absolute proof before committing to a belief can actually prevent good outcomes from happening. ## When Belief Creates Reality Consider how this works in daily life through self-fulfilling beliefs: 1. **Social Trust:** To make a new friend or start a business partnership, you must first believe that the other person is trustworthy. You lack objective proof, but holding the positive belief creates the very condition for the trust to develop. 2. **Peak Performance:** Elite athletes routinely practice visualization. A runner convinces themselves they can break a world record before they have ever achieved the times to prove it. The belief fuels the extreme effort required to make the outcome real. 3. **Hope in Crisis:** During major social movements, activists must believe that justice will prevail, even when centuries of historical evidence suggest otherwise. Without that outcome-oriented belief, the effort required to change society vanishes. If we restricted our beliefs strictly to what the current evidence guarantees, we would eliminate confidence, invention, and deep human connection. ## Expected Utility in Everyday Life In economics and decision theory, scientists evaluate choices using **expected utility**—measuring a choice by multiplying its probability by its payoff. A action with a low probability of certainty can still be completely rational if the potential benefit is massive or the cost of inaction is catastrophic. Believing in your own success, in the goodness of others, or in a higher purpose carries minimal downside, but it yields immense benefits: resilience, motivation, and mental well-being. When the consequences of a belief transform your life for the better, believing becomes the most rational thing you can do.