Ever go through a phase where you feel like every day is a Monday? You wake up, you hit snooze. Then you hit snooze again and you just don't feel it? Why? In one study, people who did a "three good things" exercise for a week felt happier and less depressed after one month. The study then did the three-month and six-month follow-ups. Not surprisingly, the happiest participants were the ones who had continued the practice throughout.