Gratitude is like a muscle. A number of studies confirm that the more we express our gratitude, the more grateful we become and the more we have a bright outlook on life. In one study of high school students, the students who showed the highest levels of gratitude had better GPAs, less depression and envy. A focus on materialism had just the opposite effect on students. An attitude of gratitude is a virtue that is more caught than taught. Parents can instill thankfulness in their children by requiring them to do chores and then thanking them for doing them (Wall Street Journal, December 23).