J. Scott Armstrong is a marketing professor at Wharton and author of the   recent book, Principles of Forecasting. In the article that follows, he talks about his research into role-playing as a tool for leaders in both business and government who face crucial decisions in situations ranging from military clashes to marketing challenges. How should the war on terrorism proceed? How will other countries respond? Since September 11, I have watched as military and political experts have described what we should do and what the consequences will be. Although these forecasts sound impressive and come with convincing arguments to support their conclusions, they are often wrong. This is not surprising; research tells us that experts are not good at forecasting decisions in conflict situations. The reason is that conflicts are complex and often involve several rounds of action and reaction. Fortunately, there is an effective alternative: role-playing.…