People are happy because of happy friends.

I dunno, I kinda wanna punch my overly-chipper friends in the nose. From Time:

Ever wonder whether happy people have something you don't, something that keeps them cheerful, chipper and able to see the good in everything? It turns out they do — they have happy friends.

That's the conclusion of researchers from Harvard and the University of California at San Diego, who report in the British Medical Journal online that happiness spreads among people like a salubrious disease. Dr. Nicholas Christakis and James Fowler studied nearly 5,000 people and their more than 50,000 social ties to family, friends and co-workers, and found that an individual's happiness is chiefly a collective affair, depending in large part on his or her friends' happiness — and the happiness of their friends' friends, and even the friends of their friends' friends.

The merriment of one person, the researchers found, can ripple out and cause happiness in people up to three degrees away. So if you're happy, you increase the chance of joy in your close friend by 25%; a friend of that friend enjoys a 10% increased chance. And that friend's friend has a 5.6% higher chance.