If you want to know whether your marriage will survive, look at your spouse's yearbook photos.
Psychologists have found that how much people smile in old photographs can predict their later success in marriage.
"Maybe smiling represents a positive disposition towards life," said study leader Matthew Hertenstein, a psychologist at DePauw University in Indiana. "Or maybe smiling people attract other happier people, and the combination may lead to a greater likelihood of a long-lasting marriage. We don't really know for sure what's causing it."
Well, smile is the cheapest way to improve one's face so I guess, you'll pretty much attract more people that constitutes larger scale of social network which can lighten some burden within marriage. So I guess, it's all about smile, eh? Now I know, why my friend is still single. Nyahaha!
Source: Smiles Predict Marriage Success