Wishful thinking is constrained by reality; people cannot believe the utterly implausible simply because they want to. Here, we uncover an exception to this basic principle of motivated cognition. We show that one goal in particular---the goal to advocate---systematically biases judgments in spite of strong countervailing evidence. This is more than a harmless delusion. Advocacy goals lead to greater endorsement of far-fetched 'crackpot' theories (Study 5), and impede performance in

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... (Study 6). These effects do not emerge from other kinds of goals: when people desire an outcome, but do not have a goal to advocate for it, reality constrains bias. Not only does this require a revision to the theoretical record, it serves as a cautionary warning to managers and other decision-makers, who are susceptible to the biasing forces of advocacy.