over-optimistic, while insisting that their current predictions are realistic. For group tasks Carter and colleagues conducted three studies in 2005 that demonstrate empirical support that the planning fallacy also affects predictions concerning group tasks. This research emphasizes the importance of how temporal frames and thoughts of successful completion contribute to the planning fallacy. Additional studies Bent Flyvbjerg and Cass Sunstein argue that Albert O. Hirschman's Hiding Hand principle is the planning fallacy writ large, and they tested the empirical validity of the principle. See also further reading below for additional studies. Proposed explanations Kahneman and Tversky originally explained the fallacy by envisaging that planners focus on the most optimistic scenario for the task, rather than using their full experience of how much time similar tasks require. Roger Buehler and colleagues account for the fallacy by examining wishful thinking; in other words, people think tasks will be finished quickly and easily because that is what they want to be the case. In a different paper, Buehler and colleagues suggest an explanation in terms of the self-serving bias in how people interpret their past performance. By taking credit for tasks that went well but blaming delays on outside influences, people can discount past evidence of how long a task should take. One experiment found that when people made their predictions anonymously, they do not show the optimistic bias. This suggests that the people make optimistic estimates so as to create a favorable impression with others, which is similar to the concepts outlined in impression management theory. Another explanation proposed by Roy and colleagues is that people do not correctly recall the amount of time that similar tasks in the past had taken to complete; instead people systematically underestimate the duration of those past events. Thus, a prediction about future event duration is biased because memory of past event duration is also biased. Roy and colleagues note that this memory bias does not rule out other mechanisms of the planning fallacy. Sanna and colleagues examined temporal framing and thinking about success as a contributor to the planning fallacy. They found that when people were induced to think about a deadline as distant (i.e., much time remaining) vs. rapidly approaching (i.e., little time remaining), they made more optimistic predictions and had more thoughts of success. In their final study, they found that the ease of generating thoughts also caused more optimistic predictions. One explanation,