He Invested Through Five Bubbles. He Wrote the Book on Them | The Weekly Wrap - 5/17/2026

This week’s Excess Returns Weekly Wrap brings together highlights from our interviews with Jeremy Grantham, Andy Constan, Edward Chancellor and Marc Rubinstein to examine AI, bubbles, private credit, market structure and the lessons of past capital cycles.We look at whether AI is creating a new investment bubble, why technological revolutions often disappoint investors even when the technology succeeds, and how private credit, financials, monopolies and market leadership fit into today’s confusing market environment.Main topics covered:• Jeremy Grantham on mean reversion, monopoly power and why the Mag 7 may have avoided normal competitive pressure• Andy Constan’s framework for bubbles, including the “something new,” escalation event and peaking phase• Edward Chancellor on AI capex, overstated demand and why boom-time profits can reverse when investment is misallocated• Marc Rubinstein on private credit, redemption gates, retail investors and why the risks may be real without being systemic• Grantham’s argument that AI may become a cost of doing business rather than a permanent boost to aggregate profits• Lessons from Long-Term Capital Management and how policy responses can add fuel to a bubble• What railway mania, canals and past technology booms can teach investors about winners, losers and overbuilding• Rubinstein’s case for European financials and why growth can be dangerous in financial services• Grantham’s bubble detector and the signal that has appeared near the tops of 1929, the Nifty Fifty, 2000 and 2021• Why investors need humility when navigating bubble regimes, AI enthusiasm, private credit and market concentrationTimestamps:00:00 Jeremy Grantham, Andy Constan and Edward Chancellor on AI, bubbles and capex01:14 Why this week’s conversations connect across AI, bubbles and market structure04:31 Jeremy Grantham on monopoly power, mean reversion and the Mag 711:24 Andy Constan’s three-stage framework for market bubbles20:12 Edward Chancellor on AI capex, overstated demand and reported profits30:28 Marc Rubinstein on private credit gates and the limits of systemic risk37:50 Jeremy Grantham on why AI may become a cost of doing business42:55 How Long-Term Capital Management helped fuel the late 1990s bubble50:02 What railways, canals and overbuilding teach us about technology booms55:58 Marc Rubinstein on European financials, innovation and US market confusion1:00:38 Jeremy Grantham’s bubble detector and the warning from market leaders1:05:59 Closing thoughts on bubble signals, investor humility and Excess Returns resources