How do experts go wrong? There are several kinds of expert failure. The most innocent and most common are what we might think of as the ordinary failures of science. Individuals, or even entire professions, get important questions wrong because of error or because of the limitations of a field itself. They observe a phenomenon or examine a problem, come up with theories and solutions, and then test them. Sometimes they’re right, and sometimes they’re wrong. ... Science is learning by doing. Laypeople are uncomfortable with ambiguity, and they prefer answers rather than caveats. But science is a process, not a conclusion. Science subjects itself to constant testing by a set of careful rules under which theories can be displaced only by other theories. Laypeople cannot expect experts to never be wrong; if they were capable of such accuracy, they wouldn’t need to do research and run experiments in the first place. If policy experts were clairvoyant or omniscient, governments would never run deficits, and wars would break out only at the instigation of madmen. ... The most important point is that failed predictions do not mean very much in terms of judging expertise. Experts usually cover their predictions (and an important part of their anatomy) with caveats, because the world is full of unforeseeable accidents that can have major ripple effects down the line. ... The goal of expert advice and prediction is not to win a coin toss, it is to help guide decisions about possible futures.