Two groups of people wereasked to write down any thoughts they had in six minutes; one was told not tothink about a specific image (in thiscase, a white bear). Afterward,individuals in both groups wentshopping with the same amount ofmoney. Those who had beenrequired to exercise self-controlspent nearly three times as much asthose allowed to think freely. Thelesson: "Your willpower is limited,"says study author Kathleen Vohs ofthe University of Minnesota. "It'shard to exercise control in more thanone major way at a time."