Your thoughts make a difference. A psychological study by Emons and McCullough – Counting Blessings versus Burdens – published in the Journal of Personality and Social Psychology 84, no.2 (2003) divided participants into three groups.
Group one was asked to list five things they were grateful for that happened in the last week. The second group, to write five things that bothered them in the last week, and the third group to write five things irrespective of being pleasurable or worrisome. This experiment lasted ten weeks.
In the grateful category, people listed things like a beautiful sunset, the generosity of friends, the chance to be alive. In the hassles condition, people included taxes, difficulty to find a parking space, letting the food overcook and so on.
People of the first group, who concentrated in uplifting thoughts, felt happier and appeared happier to their friends.