Passion may be the linchpin of grit, but it's not the only element. Ambition is right on its heels. For some of us, vowing to organize our closet next weekend may represent the height of our ambition. Truly gritty people, however, tend to set especially challenging long-term goals; one of Duckworth's students confidently stated that he planned to become a U.S. Senator. Self-discipline is probably also an important part of grit, and studies have shown that gritty people tend to be highly self-disciplined. But whereas perseverance implies the ability to keep doing something, self-discipline primarily implies the ability to refrain from doing something—to stop drinking, goofing off or straying from one's diet. It doesn't embrace the ambition and zest needed to tackle a challenging goal. "Self-discipline is probably necessary for grit," Duckworth says, "but it's not sufficient." Then there's optimism, a trait that Dean Keith Simonton of the University of California at Davis finds is extremely common among high achievers. "It helps them hang in there in times when they have to overcome all of these obstacles," he observes. "They just really believe in the end that they're going to win, and until they do, they're just going to keep on pushing, keep on making the phone calls, writing the letters, whatever they have to do." It's this optimism, most likely, that helped Chester Carlson convince someone that the technology he had invented was worthwhile, even after more than 20 companies and the National Inventors Council rejected his work. Carlson called his new process electrophotography; today it's known as photocopying.