National leaders get all sorts of advice in times of tension and conflict. But often the competing counsel can be broken down into two basic categories. On one side are the hawks: They tend to favor coercive action, are more willing to use military force, and are more likely to doubt the value of offering concessions. When they look at adversaries overseas, they often see unremittingly hostile regimes who only understand the language of force. On the other side are the doves, skeptical about the usefulness of force and more inclined to contemplate political solutions. Where hawks see little in their adversaries but hostility, doves often point to subtle openings for dialogue.

As the hawks and doves thrust and parry, one hopes that the decision makers will hear their arguments on the merits and weigh them judiciously before choosing a course of action. Don’t count on it. Modern psychology suggests that policymakers...