“We know that if you study something twice, in spaced sessions, it’s harder to process the material the second time, and so people think it’s counterproductive,” as Nate Kornell, a psychologist at Williams College, told me. “But the opposite is true: You learn more, even though it feels harder. Fluency is playing a trick on judgment.” So it is that we end up attributing our poor test results to “test anxiety” or—too often—stupidity.