Researchers discovered this phenomenon through clever experiments. In one famous study, they had people make a series of choices in a mall. One group made many decisions: which items to buy, what features they wanted, color preferences, and so on. The control group simply recorded their opinions without choosing.
Afterward, both groups performed a willpower test—holding their hand in ice water. The decision-makers gave up significantly faster. Making choices had literally weakened their ability to endure discomfort.
Think about that. Choosing between red or blue shirts affected people's physical endurance. If simple shopping decisions can deplete us this much, what is our daily decision marathon doing to us?