To be persuasive, theories must be tested on at least a few cases other than those examined in the initial development of the idea analyst may discover which factors proposed as possible causes during the discovery stage of theory building really do have general casual influence and which should be thought of as part of the “error term”
Error term: all those serendipitous, conjunctural, and other kinds of factors that contribute to particular outcomes in particular cases but that do not systematically influence outcomes