World Gratitude Day takes place on September 21, 2015. Gratitude, thankfulness, gratefulness, or appreciation is a feeling or attitude in acknowledgment of a benefit that one has received or will receive. The experience of gratitude has historically been a focus of several world religions, and has been considered extensively by moral philosophers such as Adam Smith.
Gratitude may also serve to reinforce future prosocial behavior in benefactors. For example, one experiment found that customers of a jewelry store who were called and thanked showed a subsequent 70% increase in purchases. In comparison, customers who were thanked and told about a sale showed only a 30% increase in purchases, and customers who were not called at all did not show an increase. In another study, regular patrons of a restaurant gave bigger tips when servers wrote "Thank you" on their checks.
According to Cicero, "Gratitude is not only the greatest of the virtues but the parent of all others." Multiple studies have shown the correlation between gratitude and increased wellbeing not only for the individual but for all people involved. The positive psychology movement has embraced these studies and in an effort to increase overall wellbeing, has begun to make an effort to incorporate exercises to increase gratitude into the movement. (With material from: Wikipedia)