Although most family businesses fail to last through the third generation, some are able to thrive. Why? By following four rules:  maintain good governance, identify and develop both family and nonfamily talent; pursue disciplined succession; and preserve family gravity. The last is perhaps the most difficult to get right. So Egon Zehnder and the Family Business Network International (FBNI), embarked on a three-year global study to discover what makes up family gravity. After interviewing more than 50 executives at 28 leading family businesses across the Americas, Europe, and Asia and surveying of 4,000 FBNI members, they concluded that gravity has six dimensions:  values and vision, the right involvement, cohesion and interaction, family governance and clarity on leadership principles and roles.