Imagine two individuals, Alex and Ben, who both plan to start a strict diet and exercise regimen on Monday. On Monday morning, Alex decides not to start because they receive an unexpected invitation to a week-long food festival with a friend visiting from out of town. Ben, on the other hand, wakes up on Monday and, despite having no new plans or external changes, decides to postpone the diet until the following week, feeling that the immediate sacrifice of his favorite foods is too great. Analyze the decisions of both individuals. Which person's behavior is a clear example of a failure of willpower due to shifting preferences over time, and why? Explain the key difference in the underlying reasons for their failure to follow through with their original plans.