In the modern era, the executive branch has extraordinary information‐gathering advantages over the legislative and judicial branches. As a result, it will often know immeasurably more than they do, both on domestic issues and on foreign affairs. In general, it also has a strong system of internal checks and balances, reducing (though certainly not eliminating) the risk of factual error. Because the executive is the most knowledgeable branch, it often makes sense, within constitutional boundaries, to give it considerable discretion in both domestic and foreign affairs and to grant it considerable (though hardly unlimited) deference when it exercises that discretion. Both legislators and judges tend to be insufficiently aware of their epistemic disadvantages. The argument for restricting executive discretion depends on suspicion about the biases and motivations of the most knowledgeable branch and about its failure to give sufficient respect to liberty, and an associated fear of some form of “groupthink,” usually in the form of group polarization. In some times and places that suspicion is extremely important, but it is hazardous to invoke it as a basis for confining the authority of those who have the most knowledge. These points are illustrated with close reference to the debate over the Department of Transportation’s rear visibility rule, proposed in 2010 and finalized in 2014.