The field of positive psychology, founded by Martin Seligman, a professor at the University of Pennsylvania, has focused on trying to identify things that can lead to lasting changes in happiness levels. This research has yielded a number of useful insights: simple positive activities such as practicing gratitude, performing random acts of kindness, or reliving positive events from your past really do seem to make people happier if practiced regularly. But even these things seem susceptible to the treadmill effect. Over time, the impact they have on your happiness gradually diminishes.