The question with which Smith, Bruner and White (1956) began their classic Opinions and Personality over 50 years ago is still appropriate today, albeit with a change in the pronoun: “Of what use to man are his opinions?” (for further discussion on Smith, Bruner and White see: 1; Eagly and Chaiken 1998: 303-309; George 1958; Hammond 1996: Ch. 11; Herek 1987; Katz 1960; Sarnoff and Katz 1954; Tetlock 2002). I think their answer was essentially correct as well: People adopt opinions not only to understand the world, but also to meet the psychological and social needs to live with themselves and others. In this chapter I use this basic insight to examine some of the puzzles in what people believe generally, drawing most of my examples from the realm of international politics. I believe these insights cast light on what many people assume to be intentional “threat inflation.” I recognize that proving that actors actually believed in what they were doing at the time is a monumental challenge, one that even access to private conversations and records of the time cannot reliably solve. Attempting to sort out sincere beliefs from intentional threat inflation is a necessary knot to disentangle as best we can, however, because it is a fundamental question for foreign-policy making – are grievous foreign policy errors primarily unavoidable outcomes of sincere beliefs and misperceptions or the result of intentional deception on the part of political leaders? I propose here ideas about how to determine if beliefs caused behavior – i.e., if beliefs are powerful and autonomous as opposed to ex post rationalizations for behavior. If beliefs cause behavior, as my study of history suggests they often do, then the problem of steering clear of beliefs such as the domino theory, the acceptability of slavery or belief in Saddam Hussein’s hiding of weapons of mass destruction in Iraq – beliefs known to be wholly wrong-headed with the benefit of hindsight – will be much more difficult than is suggested by those who argue that politicians are intentionally deceiving the public with selfserving policies such as threat inflation and need to be kept politically and bureaucratically in check.