Only about 12% of family-owned businesses make it to a third generation still under family control, according to a new Goldman Sachs playbook aimed at the founders and dynasties the bank counts among its most prized clients. It’s a statistic Goldman itself put in print in “Honoring Legacy and Positioning for the Future,” a paper shaped by senior leaders across its Investment Banking and Private Wealth Management divisions.

To dig into the thinking behind it, Fortune put a series of questions to François-Xavier de Mallmann, chairman of Goldman Sachs’ Investment Banking division and chairman of Goldman Sachs EMEA — the banker steering Goldman’s relationships with many of the world’s largest family-controlled enterprises. His answers, lightly edited for length, get at something the playbook’s five-question framework can’t fully capture on its own: that the biggest threat to a family business isn’t usually a missing legal document. It’s optimism.

Your paper says only 12% of family businesses make it to a third generation. Why is the success rate still so low?

Founder and family-controlled companies are major contributors to the global economy. Decisions around succession and ownership are among the most consequential they will make, and both have a significant impact on the business and the family. Goldman Sachs has a dedicated effort focused on serving family-owned businesses and founders around the world, working across our Global Banking & Markets and Asset & Wealth Management divisions.