What is the cause and result of the roseto mystery? what overarching idea is gladwell establishing in his introduction?

Roseto, a town in Pennsylvania. People of the town are mostly Obese but the occurrence of heart disease in them are very low. This amazed the doctors and they performed every kind of tests but this became a mystery. 
The result of the mystery was the social culture of the community.
People of the town happily lived together, sometimes three generations of a family would live under one roof, all are good with their neighbors and chat with them.