A successful operation is the interplay of thousands of variables. If only we could find which variables could assure success, then our decisions as managers would be clear. This is what authors of popular business books, such as Built to Last and In Search of Excellence, set out to do. By interviewing successful companies and then finding attributes they all had in common, the authors posited that because these companies shared traits, the traits, therefore, must cause success. In reality, it is impossible to say which variable is causing which outcome. This is why the scientific method demands control groups, studying one variable at a time and assuring studies are blind. Without the ability to do this, the next best proof of a theory is the test of time.