He Invested Through Five Bubbles. He Wrote the Book on Them | What We Learned This Week
Two Quants and a Financial PlannerMay 17, 202601:08:08

He Invested Through Five Bubbles. He Wrote the Book on Them | What We Learned This Week

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.

Full episodes:

Jeremy Grantham
https://youtu.be/tEQQaJQxBMs

Andy Constan
https://youtu.be/XXS28h0Jvh0

Edward Chancellor
https://youtu.be/X8seA57CwCo

Marc Rubinstein
https://youtu.be/tEL92UnZW5o

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 concentration

Timestamps:

00:00 Jeremy Grantham, Andy Constan and Edward Chancellor on AI, bubbles and capex
01:14 Why this week’s conversations connect across AI, bubbles and market structure
04:31 Jeremy Grantham on monopoly power, mean reversion and the Mag 7
11:24 Andy Constan’s three-stage framework for market bubbles
20:12 Edward Chancellor on AI capex, overstated demand and reported profits
30:28 Marc Rubinstein on private credit gates and the limits of systemic risk
37:50 Jeremy Grantham on why AI may become a cost of doing business
42:55 How Long-Term Capital Management helped fuel the late 1990s bubble
50:02 What railways, canals and overbuilding teach us about technology booms
55:58 Marc Rubinstein on European financials, innovation and US market confusion
1:00:38 Jeremy Grantham’s bubble detector and the warning from market leaders
1:05:59 Closing thoughts on bubble signals, investor humility and Excess Returns resources