It’s theoretically possible that your life is just an elaborate dream sequence. Do you know that you're not merely dreaming? Of course you do! Yet radical skepticism remains a serious topic in philosophy and popular culture, including successful films such as The Matrix and Vanilla Sky. Why is skepticism tempting, despite our better judgment? My lab discovered that it is partly due to two psychological factors that interact in an unexpected way. First, humans evaluate inferential belief more harshly than perceptual belief. Second, humans evaluate inferential belief more harshly when its content is negative (something is not true) than when it’s positive (something is true). Skeptics focus our attention on negative inferential beliefs, and we are biased against this combination of source and content. The skeptic sows seeds of doubt by exploiting this feature of our psychology.