“Quantum mechanics is the most useful and powerful theory physicists have ever devised. Yet today, nearly 90 years after its formulation, disagreement about the meaning of the theory is stronger than ever. New interpretations appear every year. None ever disappear. … The message from QBism is this: You needn't feel guilty about never getting nervous about this stuff. You were right not to be bothered. But for the sake of intellectual coherence, you had better reexamine what you wrongly may have thought you understood perfectly well about the nature of probability.”