A study examined and tested the knowledge sources individuals tap in the planning process and the process of plan modification. It is expected that contrary to plan-based theories, individuals will fail to remediate flaws in their plans if given the chance to develop a plan to pursue the same goal. It is also expected that differences exist between individuals' planned and actual performances as measured by the knowledge sources used in the respective planning procedures. Finally, it is expected that providing participants with arguments for a persuasion goal will validate the assumption that role model knowledge is a primary source of knowledge in planning to reach persuasive goals. Subjects, 15 communication students at a midwestern university took part in 2 sessions spaced 2 weeks apart from each other. At the first session they were asked to participate in two scenarios. In the first, they were to ingratiate themselves with a new roommate. In the second, they were to persuade another person to accept their view as to whether or not alcohol should be allowed in the dormitories. At the second session, they were given the same two problems and asked to talk through them aloud into a tape recorder. As expected, the results showed no consistent relationship between success and failure of a plan and plan modification. Findings raise questions about the adequacy of humans as planners and basic assumptions of the plan modification model. (Contains 5 tables of data and 15 references.) (TB)