In decision making and psychology, decision fatigue refers to the deteriorating quality of decisions made by an individual, after a long session of decision making. It is now understood as one of the causes of irrational trade-offs in decision making. For instance, judges in court have been shown to make less favorable decisions later in the day than early in the day. Decision fatigue may also lead to consumers making poor choices with their purchases.
There is a paradox in that "people who lack choices seem to want them and often will fight for them"; yet at the same time, "people find that making many choices can be [psychologically] aversive."
Reduced ability to make trade-offs
Trade-offs, where either of two choices have positive and negative elements, are an advanced and energy-consuming form of decision making. A person who is mentally depleted becomes reluctant to make trade-offs, or makes very poor choices. Jonathan Levav at Stanford University designed experiments showing how decision fatigue can leave a person vulnerable to sales and marketing strategies designed to time the sale. "Decision fatigue helps explain why ordinarily sensible people...can't resist the dealer's offer to rustproof their new car." 
Dean Spears of Princeton University has argued--albeit without any scientific evidence--that decision fatigue caused by the constant need to make financial trade-offs is a major factor in trapping people in poverty. Given that financial situations force the poor to make so many trade-offs, they are left with less mental energy for other activities. "If a trip to the supermarket induces more decision fatigue in the poor than in the rich — because each purchase requires more mental trade-offs — by the time they reach the cash register, they’ll have less willpower left to resist the Mars bars and Skittles. Not for nothing are these items called impulse purchases."
Decision fatigue can result not only in fast and careless decisions but even in decision avoidance, where no decision is made at all.  Research by Iyengar and Lepper (2000) "found that people who had more choices were often less willing to decide to buy anything at all, and their subsequent satisfaction was lower when they had been confronted with 24 or 30 options than when they faced six options"; which "suggest[s] that choice, to the extent that it requires greater decision-making among options, can become burdensome and ultimately counterproductive." In the formal approach to decision quality management, specific techniques have been devised to help managers cope with decision fatigue. Other forms of decision avoidance used to bypass tradeoffs and the emotional costs of decision making can include selecting either the default, or status quo options, where these are available.
Decision fatigue can influence irrational impulse purchases at supermarkets. During a trip to the supermarket, trade-off decisions regarding prices and promotions can produce decision fatigue, hence by the time the shopper reaches the cash register, less willpower remains to resist impulse purchases of candy and sugared items. Sweet snacks are usually featured at the cash register because many shoppers have decision fatigue by the time they get there. Florida State University social psychologist Roy Baumeister has also found that it is directly tied to low glucose levels, and that replenishing them restores the ability to make effective decisions. This has been offered as an explanation for why poor shoppers are more likely to eat during their trips.
Researcher Carol Dweck found "that while decision fatigue does occur, it primarily affects those who believe that willpower runs out quickly." She states that "people get fatigued or depleted after a taxing task only when they believe that willpower is a limited resource, but not when they believe it's not so limited". She notes that "in some cases, the people who believe that willpower is not so limited actually perform better after a taxing task."
The "process of choosing may itself drain some of the self’s precious resources, thereby leaving the executive function less capable of carrying out its other activities. Decision fatigue can therefore impair self-regulation". "[S]ome degree of failure at self regulation" is at the root of "[m]ost major personal and social problems", such as debt, "underachievement at work and school" and lack of exercise.
George Loewenstein has suggested that the disastrous failure of men in high office to control impulses in their private lives may at times be attributed to decision fatigue stemming from the burden of day-to-day decision making. Similarly, Tierney notes that "C.F.O.'s [are] prone to disastrous dalliances late in the evening", after a long day of decision-making.
With regard to self-regulation in legal regulation: One research study found that the decisions judges make are strongly influenced by how long it has been since their last break. "We find that the percentage of favorable rulings drops gradually from ≈65% to nearly zero within each decision session and returns abruptly to ≈65% after a break."
- Tierney, John (August 21, 2011). "Do You Suffer From Decision Fatigue?". New York Times Magazine. Retrieved August 23, 2011.
- Baumeister, Roy F (2003), "The Psychology of Irrationality", in Brocas, Isabelle; Carrillo, Juan D, The Psychology of Economic Decisions: Rationality and well-being, pp. 1–15, ISBN 0-19-925108-8.
- Danzigera, Shai; Levav, Jonathan; Avnaim-Pesso, Liora (2011), "Extraneous factors in judicial decisions", Proceedings of the National Academy of Sciences 108 (17): 6889–6892, doi:10.1073/pnas.1018033108.
- Vohs, Kathleen; Baumeister, Roy; Twenge, Jean; Schmeichel, Brandon; Tice, Dianne; Crocker, Jennifer (2005). Decision Fatigue Exhausts Self-Regulatory Resources — But So Does Accommodating to Unchosen Alternatives.
- "Decision Fatigue Saps Willpower — if We Let It". Time. August 23, 2011.
- Anderson, Christopher (2003). "The Psychology of Doing Nothing: Forms of Decision Avoidance Result from Reason and Emotion". Psychological Bulletin 129: 139–167.
- Saxena, PK (2009), Principles of Management: A Modern Approach, p. 89, ISBN 81-907941-5-9.
- Mawby, William D (2004), Decision process quality management, p. 72, ISBN 0-87389-633-5.
- Baumeister, Roy (2002). "Ego Depletion and Self-Control Failure: An Energy Model of the Self’s Executive Function". Self and Identity 1 (2): 129–136. doi:10.1080/152988602317319302.
- Loewenstein, George (2003), Time and decision: economic and psychological perspectives on intertemporal choice, p. 208, ISBN 0-87154-549-7.