Recent research has revealed that mood of a person is strongly affected by the people around him. Research team led by Dr Nicholas Christakis, a sociologist at Harvard Medical School, and including Professor Fowler analyzed 53,228 social connections between 5,124 individuals over time.
Researchers said that how grumpy people feel can be influenced not only by the state of mind of those closest to us, but also by friends of friends that we have never met like ripples from "pebbles thrown into a pond".