U.S. stocks have just pulled off a trifecta that almost never happens, a pattern that has appeared only a handful of times in roughly 155 years of modern market history. Each time, the aftermath has followed a strikingly similar script, tempting investors to believe that the next chapter is already written. I want to unpack what this rare setup actually is, how previous instances played out, and why the historical record is both encouraging and more complicated than the headline suggests.
What the “three in 155 years” pattern really means
The starting point is the extraordinary run investors watched through 2025, when The Dow Jones Industrial Average, the S&P 500, and the Nasdaq Composite all surged in tandem and pushed to repeated highs. In the current cycle, that strength has translated into a configuration that market historians say has only appeared three times in about 155 years, tying together powerful price momentum with unusually rich valuations across the major benchmarks. In earlier episodes, similar surges in the S&P 500 and its peers were followed by multi‑year stretches in which equities continued to advance, even as volatility picked up and leadership shifted beneath the surface, a pattern that is now being cited as a roadmap for 2026 and beyond according to analysis of the 155 years of data.
What makes the current setup so distinctive is not just that indexes are near records, but that they have done so while valuations, measured against long‑run earnings, have climbed into territory that has historically been rare. Earlier periods that looked similar combined strong trailing returns in the S&P 500 with valuation gauges that were already stretched, yet the market still managed to grind higher before any serious reset. That is the historical pattern now being invoked when analysts argue that the latest surge in the S&P 500 and the broader 500‑stock universe could have further to run, even if the easy gains are behind it.
The “historically flawless” valuation signal
Momentum alone does not explain why this pattern has investors’ attention, and I see the valuation backdrop as the second crucial piece. Nov research into long‑term valuation tools highlights that, However impressive the recent rally has been, one particular metric has stood out as a “historically flawless” guide to long‑run returns, consistently flagging when the market was priced for disappointment. That measure, which compares current prices to inflation‑adjusted earnings over an extended period, is now flashing a warning that the S&P 500 is trading at a premium that has rarely been sustained, a signal that has previously preceded weaker forward returns even when the near‑term tape still looked strong, according to this valuation work.
Widening the lens, other analysts have focused on the Shiller version of the price‑to‑earnings ratio, which smooths profits over a decade to filter out the business cycle. Widening the historical window shows that when the Shiller measure for the S&P 500 has pushed above 30 and stayed there, it has only happened a handful of times in roughly 154 years, and each of those episodes eventually gave way to a period of much lower subsequent returns for the 500 (S&P 500 Index). That context, drawn from a review of the Shiller data, reinforces the idea that today’s setup is not just about price strength, but about how far valuations have stretched relative to their own history.
Postwar precedents: when the S&P 500 keeps winning
To understand what “always did the same thing next” really implies, I look at the postwar record for the S&P 500 specifically. Dec analysis of the SNPINDEX listing for the S&P 500, identified by the ticker GSPC, notes that the index is on track to close another banner year, which would mark the third time since the postwar era that it has delivered such a strong multi‑year run. In the two prior cases, the S&P 500 (SNPINDEX: ^GSPC) did not immediately roll over; instead, it continued to generate positive returns in the following year, albeit at a more modest pace, suggesting that powerful uptrends can persist even after they look statistically stretched, a pattern highlighted in recent postwar studies.
Another way to frame the same idea is to look at streaks rather than calendar years. Key Points The S&P 500 ( S&P 500 Index ) (SNPINDEX: ^GSPC) is described as being in “rarified air” after climbing for three straight years and starting 2026 near an all‑time high. After those kinds of three‑year winning streaks, history shows that the index has only twice before been this extended in the last 45 years, and in both of those prior instances, the following year still produced gains, even if they were smaller and more volatile. That track record, drawn from a review of the three‑year streaks, is the core of the bullish case that “this time” may rhyme with the past, even if it does not repeat perfectly.
Why today’s setup looks even rarer than usual
What makes the current environment especially unusual, in my view, is that it combines those momentum streaks with valuation extremes that are themselves historically scarce. Dec research into long‑term market momentum notes that the recent rally has pushed the market into territory that has only been seen twice over roughly 153 years, with the latest surge in prices creating a configuration that blends strong trailing returns with elevated valuation readings. This market momentum has led to the stock market doing something witnessed only twice over the past 153 years, and history is described as being “very clear” about what followed, with subsequent returns eventually cooling even if they did not collapse immediately, a pattern documented in the 153 year record.
At the same time, valuations across global markets have reached levels that have only appeared a few times since the late nineteenth century. Nov analysis of long‑run price‑to‑earnings ratios points out that, Since 1870, the average price‑to‑earnings ratio for the U.S. stock market has been roughly 16, with the median over that period close to that same level, yet today’s readings sit far above those long‑term norms. That work also notes that markets are historically very expensive relative to their own past, and that timing the exact moment of a reversal has proven extremely difficult, a tension that is central to the current debate over whether investors should be worried according to this review of long‑term averages.
What history suggests investors should actually do
For investors trying to translate all of this into action, the temptation is to treat the “three in 155 years” pattern as a guarantee that the next year will look like the last two historical examples. I think the more responsible reading is that history narrows the range of likely outcomes without eliminating risk. Dec research into prior episodes when stock markets did something they had only done three times since 1948, including stretches like 1984‑1985 and 1995‑1996, shows that a unique set of circumstances caused those events to coincide and that they were unlikely to repeat exactly. Those earlier cycles still rewarded patient investors, but they also featured sharp pullbacks and sector rotations that punished anyone who assumed that past averages would apply neatly to every part of the market, a nuance highlighted in the review of 1948 onward.
That is why I see the current setup as a call for discipline rather than bravado. The historical record around the S&P 500 and the broader 500‑stock universe suggests that rare combinations of strong momentum and rich valuations have often been followed by more gains, but also by lower future returns and higher volatility. For long‑term investors, that argues for staying invested while gradually tilting toward quality balance sheets, durable cash flows, and reasonable earnings multiples, instead of chasing whatever has led the latest leg higher. The past three instances in roughly 155 years may rhyme with today, but the next chapter will still be written in real time, not by a statistic.
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