"Robert Emmons, a psychologist at the University of California, at Davis, divided 1,000 adults into three groups. For one week, all of them kept a daily journal rating their moods. The first group had no additional assignment. The second group listed things that annoyed them each day. The third group kept a list of all the things they were thankful for each day.
The people in group three didn’t start out more grateful than their counterparts in the control groups. They adopted a new habit. They noticed all that was good and right in their lives, all the support and love they received. Nothing else changed in their lives. Those who kept gratitude journals merely shifted where they put their attention. After just one week, those who kept gratitude journals felt better about their lives as a whole, and reported themselves as being more alert and enthusiastic about everything." (http://www.4therapy.com/consumer/life_topics/article/8682/113/Is+it+Selfish+to+Want+to+Be+Happier%3F)