India, June 27 -- The Stoics, Ancient Greek philosophers, wrote for a world of tyrants and plagues.

Robert Rosenkranz, a pioneer in the world of private equity, writes for a world of unicorn IPOs and digital assets, overflowing inboxes and social-media detoxes. But the central questions haven't changed: What is in your control? What really matters? What do you owe? What is a life well-lived?

There is a straight line to be drawn from Seneca's counsel in the 1st century CE to Rosenkranz's modern reflections in his new book, The Stoic Capitalist: Advice for the Exceptionally Ambitious (Bloomsbury; May). The latter is Stoicism minus the sandals, contextualised for the contemporary world.

If this school of thought was born on the stoas or p...