Reference class forecasting or comparison class forecasting is a method of predicting the future by looking at similar past situations and their outcomes.
and Tversky found that human judgment is generally over optimistic (See: Daniel Kahneman. People tend to underestimate the costs, completion times, and risks of planned actions, whereas they tend to overestimate the benefits of those same actions. (so called inside view). A more accurate way is to predict the future by looking at similar past situations and their outcomes. (so called outside view)Overconfidence