Latest / Bull Market Conversations with Fexingo: Rallies, Momentum, and Riding Market Strength / Why Bull Markets Make Passive Indexing a Trap
Transcript
- Lucas: The S&P 500 just hit 7,354. The Nasdaq crossed 25,000. And passive index funds are taking in money at a record pace — something like four hundred billion dollars in the first half of 2026 alone. But here's the uncomfortable question that almost nobody in the bull market wants to ask: what if the most popular investment strategy of our era is actually setting you up for a much worse downturn? Luna: You're talking about passive indexing. And I know the standard rebuttal — low fees, tax efficiency, you can't beat the market. So what's the catch? Lucas: The catch is that 'the market' isn't what most people think it is. A cap-weighted index like the S&P 500 doesn't own five hundred companies equally. It owns the biggest companies the most. Right now, the top five stocks — Apple, NVIDIA, Microsoft, Amazon, Alphabet — make up about 27 percent of the entire index. Luna: That's the highest concentration since the dot-com peak in 2000, if I remember correctly. Lucas: Exactly. In March of 2000, the top five were about 18 percent. Today it's 27. So when you buy a total market ETF or an S&P 500 fund, you are effectively making a gigantic bet that the mega-cap tech winners of the last five years will keep winning forever. Luna: And that works great in a bull market like this one. But the moment those names stumble — or if the market leadership rotates into sectors that barely register in the index — the passive investor has zero ability to adjust. Lucas: Zero. That's the point. You own whatever the index says you own. And because of how cap weighting works, when a stock rises, the fund buys more of it automatically. It's a momentum feedback loop. In a narrow rally like we're seeing in 2026 — where most of the gains come from ai related tech and a handful of mega-caps — that loop amplifies concentration. Luna: Let's put a real number on it. If you have a hundred thousand dollars in an S&P 500 index fund today, roughly twenty-seven thousand dollars is riding on just five companies. That's not diversified. That's a concentrated bet with a diversified label. Lucas: And those five companies trade at an average price to earnings ratio north of 35. So you're also making a concentrated bet on high valuations persisting. Jeremy Grantham — the investor known for calling the 2000 and 2008 bubbles — just said last week that this is the most expensive market in American history. He's not talking about the average stock. He's talking about the cap-weighted index. Luna: Which is where the equal-weight version of the S&P 500 becomes interesting. The Invesco S&P 500 Equal Weight ETF, ticker r s p, weights every company the same. Its performance this year has lagged the cap-weighted index by a wide margin — because it underweights the mega-cap winners. But that's exactly the point: it's a different bet. Lucas: Right. In the equal-weight index, the top five stocks each get about 0.2 percent, same as the smallest companies. So your hundred thousand dollars has only about a thousand dollars in Apple, a thousand in NVIDIA, and so on. That's real diversification. But it means you've missed out on the massive run-up in those names. So the question for investors is: do you believe the current leadership will persist, or do you think mean reversion is coming? Luna: History suggests mean reversion is more likely than not. After the dot-com bust, the equal-weight S&P 500 dramatically outperformed the cap-weighted version for several years. The same happened after the 2008 financial crisis when financials and energy rotated back. The passive investor who stayed in a cap-weighted index through those periods experienced the full drawdown and then a slow recovery. Lucas: Look, I'm not saying passive indexing is bad. For most people, a low-cost index fund is still the best option. But I think the conversation has become religious — 'you can't beat the market, so don't try' — and that shuts down any discussion of strategy. The reality is that the market's returns are not evenly distributed. When you buy a cap-weighted index, you are making a very specific set of assumptions about the future. Luna: And one of those assumptions is that the biggest companies will keep getting bigger. That has been true for the last decade, but it wasn't true in the 1970s or the 2000s. The Nifty Fifty stocks of the 1960s and 70s — think Polaroid, Xerox, Eastman Kodak — were supposed to be invincible too. Most of them underperformed for years. Lucas: That's the historical parallel that gives me pause. The top ten companies in the S&P 500 today have a combined market cap of over twelve trillion dollars. That's roughly the size of the entire Chinese stock market. If those ten stocks collectively lose even 20 percent of their value, that's two and a half trillion dollars in losses — and the passive investor has no way to avoid it. Luna: So what's the alternative for someone who wants to stay invested but doesn't want to go full active manager? You mentioned equal weight. There's also factor-based strategies — value, momentum, quality, size — that can be implemented through ETFs with relatively low fees. Lucas: Yeah, and I think a blended approach makes a lot of sense. You could keep a core passive allocation but tilt some percentage toward equal weight, or toward small-cap value, or international. The key is to break the automatic assumption that the cap-weighted index is the default 'market portfolio' that everyone should hold. It's a choice, not a law of nature. Luna: And that choice comes with real consequences. The bull market of 2026 has been remarkably narrow. Even with the S&P 500 up year-to-date, the median stock in the index has actually underperformed the average by a wide margin. If you own only the cap-weighted index, you're effectively saying the narrow leadership will continue. Lucas: Which it might. But betting your entire retirement on that single outcome is a risk that most people don't realize they're taking. The irony is that passive investing was supposed to eliminate stock-picking risk. Instead, it replaces it with concentration risk — and concentration risk is the hardest kind to see because it feels like safety. Luna: I think that's the crucial insight. It's not that passive is wrong. It's that passive without awareness of what you actually own is dangerous. And right now, most people have no idea that their 'diversified' portfolio is essentially a leveraged bet on five tech companies. Lucas: One thing we try to do on this show is help people think about their money decisions more clearly. And a handful of listeners have told us those conversations are worth chipping in a couple bucks a month to keep going — through buy me a coffee dot com slash fexingo. That support is what keeps this ad-free and lets us dig into topics like this without worrying about selling anything. Luna: Yeah, and we really appreciate it. It's a small group, but it makes a big difference. So if you've gotten something useful out of these episodes, that's the way to keep them coming. Lucas: Alright — back to the concentration problem. One thing that's worth watching is the flow data. Despite the record inflows into passive funds, we're also seeing a quiet shift among institutional investors. Pension funds and endowments are starting to allocate more to systematic strategies that explicitly limit concentration. Luna: Right — there's a growing category called 'concentration-aware indexing' where the manager caps any single stock at, say, 5 percent of the portfolio, regardless of its market cap. That's a small but telling sign that even the passive world is starting to acknowledge the risk. Lucas: And some of the largest ETF providers are launching products that target specific factors while maintaining a broad market exposure. So you can get something like a low-volatility S&P 500 ETF that overweights less-risky stocks and underweights the high-flying ones. The trade-off is you'll lag in a roaring bull market, but you might hold up better in a correction. Luna: Which brings us back to the core question every investor should ask themselves: what am I really betting on? If you're comfortable betting on mega-cap tech momentum, the cap-weighted index is fine. But if you think the market might look different in five years — if semiconductors cycle down, if AI hype fades, if regulation increases — then maybe a different approach makes sense. Lucas: I think the most honest answer is that nobody knows. But the structure of your portfolio should reflect that uncertainty. Holding only one type of index is a bet. Diversifying across strategies — cap-weighted, equal-weighted, value, international — is a hedge against your own ignorance. Luna: And that's the kind of humility that tends to serve investors well over the long run. The bull market of 2026 feels great. But the best preparation for the next downturn is acknowledging that the current winners won't always be the winners. Lucas: Exactly. So if you're listening and you have an S&P 500 index fund in your 401k, don't panic. But maybe take ten minutes to look at what's actually inside it. Check the top ten holdings and their weightings. Ask yourself if you'd be comfortable putting that much of your savings into those specific stocks. Because that's what you're doing — whether you realize it or not. Luna: And that awareness alone puts you ahead of most investors. It's not about timing the market. It's about understanding the risk you're taking.