Image theory has been proposed as a descriptive model of decision making. The present work examines the sufficiency of a simple counting rule as a theoretical description of the assessment of compatibility, a central construct in the theory. The research was done in the context of executives assessing the compatibility between plans for reaching a specified goal and the principles that guide the operation of their respective firms. First, for each firm an expert‐system simulation was performed using Image Theory as the ‘expert’, the firm's guiding principles as the criteria, and the counting rule as the assessment procedure. This yielded a simulated compatibility assessment for each plan for each firm. Executives from each firm also assessed the compatibility of each plan with their own firm's operating principles. The assessments from the simulation were then compared with those made by the executives. The results support the descriptive sufficiency of the simple counting rule and recommend its tentative incorporation into image theory.