At the end of every day, as you go home from work or put your head on the pillow, your thoughts are likely to be full of what you didn’t do or haven’t achieved. Scientists call this the Zeigarnick Effect. It may have evolutionary value, making sure you complete things, but can leave you feeling pretty unhappy. For the next two weeks, here’s your challenge. At the end of every day, write down the three best things that happened and note the part you played in bringing each about. Research shows that this habit lifts mood and well-being.