taking the average percentage of expenditures in terms of income from ages 25 to 54 (77.7%) and multiplying such by income to arrive at a theoretical expenditure. The calculation is only applied to this age group because of unpredictable income before 25 and after 54 due to school and retirement. Food waste When buying food, people often wrongly project what they will want to eat in the future when they go shopping, which results in food waste. Major sources of error in motivation Motivated reasoning Generally, affect is a potent source of motivation. People are more likely to pursue experiences and achievements that will bring them more pleasure than less pleasure. In some cases, affective forecasting errors appear to be due to forecasters' strategic use of their forecasts as a means to motivate them to obtain or avoid the forecasted experience. Students, for example, might predict they would be devastated if they failed a test as a way to motivate them to study harder for it. The role of motivated reasoning in affective forecasting has been demonstrated in studies by Morewedge and Buechel (2013). Research participants were more likely to overestimate how happy they would be if they won a prize, or achieved a goal, if they made an affective forecast while they could still influence whether or not they achieved it than if they made an affective forecast after the outcome had been determined (while still in the dark about whether they knew if they won the prize or achieved the goal). In economics Economists share psychologists' interests in affective forecasting insomuch as it affects the closely related concepts of utility, decision making, and happiness. Utility Research in affective forecasting errors complicates conventional interpretations of utility maximization, which presuppose that to make rational decisions, people must be able to make accurate forecasts about future experiences or utility. Whereas economics formerly focused largely on utility in terms of a person's preferences (decision utility), the realization that forecasts are often inaccurate suggests that measuring preferences at a time of choice may be an incomplete concept of utility. Thus, economists such as Daniel Kahneman, have incorporated differences between affective forecasts and later outcomes into corresponding types of utility. Whereas a current forecast reflects expected or predicted utility, the actual outcome of the event reflects experienced utility. Predicted utility is the "weighted average of all possible outcomes under certain circumstances." Experienced utility refers