# Episode 390: The "AI Bubble" and Stock Market Concentration

Page: https://stenobird.com/podcast/the-rational-reminder-podcast-743537/episode-390-the-ai-bubble-and-stock-market-concentration
Text version: https://stenobird.com/podcast/the-rational-reminder-podcast-743537/episode-390-the-ai-bubble-and-stock-market-concentration.md
Podcast: [The Rational Reminder Podcast](https://stenobird.com/podcast/the-rational-reminder-podcast-743537)
Published: 2026-01-01T10:30:00+00:00
Episode link: https://rationalreminder.libsyn.com/episode-390-the-ai-bubble-and-stock-market-concentration
Audio file: https://dts.podtrac.com/redirect.mp3/traffic.libsyn.com/secure/rationalreminder/RR_-_EP.390_-_AUDIO_V2.mp3?dest-id=763774
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JSON: https://stenobird.com/v1/public/podcasts/the-rational-reminder-podcast-743537/episodes/episode-390-the-ai-bubble-and-stock-market-concentration
Duration seconds: 4220

## Resource

In this first episode of 2026, we sit down for a deep dive into one of the hottest concerns coming from clients and listeners lately: Is the U.S. stock market dangerously concentrated—and are we in an AI bubble? Ben, Dan, and Ben unpack the data, the history, and the psychology behind today's valuations, drawing lessons from past episodes of market euphoria such as Nortel in Canada, the dot-com boom, and Japan's 1989 peak. They explain why high market valuations—not concentration—pose the bigger challenge, how bubbles historically fuel real economic innovation while hurting investors, and why diversification continues to offer the only reliable protection against unknowable futures. Along the way, they revisit examples of how value stocks, small-cap value, and global diversification have fared across different market regimes. Key Points From This Episode: (0:00:40) What RR is about: evidence-based insights, synthesis episodes, expert interviews, and long-form inquiry — not debates. (0:04:20) Why listeners value RR: transparency, friendly inquiry, returning to topics over time, and the hosts' dynamic. (0:09:25) Rising concern: clients asking whether U.S. market concentration and an AI bubble mean it's time to exit stocks. (0:11:10) Advisors echo similar worries: U.S. politics, all-time highs, and emotional decision-making. (0:14:20) Today's data point: Top seven U.S. stocks = 36% of S&P 500; 32% of the total U.S. market — highest on record. (0:16:10) Why people fear concentration: a decline in the Magnificent Seven could meaningfully drag down the index. (0:17:30) Canada's cautionary tale: Nortel once hit 36% of the TSX — collapsed to zero — but the market recovered by 2005. (0:21:20) Bubbles through history: canals, railways, fiber optics, dot-coms — innovation fun…

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## Transcript

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