History is replete with well-intentioned actions and policies that have resulted in dramatic unintended consequences. We review evidence that several psychological biases result in an overly narrow focus on the intended consequences of acts and, consequently, tendencies to ignore or give too little weight to potential unintended consequences. First, a motivated desire for the intended consequences of acts can blind people to the likelihood of alternative possibilities. We review evidence that people process information and evidence in biased ways, leaving them overconfident that the desired consequences will come to pass. Second, even in the absence of motives regarding potential consequences, biases in cognition lead people to focus their attention narrowly on intended consequences in a way that limits their consideration of important alternative, unintended consequences. We review how biases toward focalism and anchoring contribute to a failure to foresee unintended consequences. Finally, we review evidence that subtle manipulations of both motivation and attention can be used to increase the focus and weight given to potential unintended consequences and, consequently, improve anticipation.