高估值時代的複利危機，美股會迎來新的「失落十年」嗎？

Original title: When the Decade Goes Missing

Original author: AdvisorAnalyst Editorial Team

Original translation: Peggy, BlockBeats

Editor's note: The belief in holding stocks for the long term is often built on a sufficiently long time scale: as long as the cycle is extended, the market will eventually reward patience. But for real investors, time is not an abstract variable. Retirement, cash flow, redemption pressure, and emotional fluctuations can all turn "long-term average returns" into a promise that is not always kept.

Based on 155 years of US stock market history, this article reviews three periods of prolonged actual return stagnation: 1929-1954, 1966-1982, and 2000-2013. It points out that the so-called "lost decade" is not a historical anomaly but a recurring structural phase of the equity market. These periods collectively account for about 35% of market history since 1871, bringing not just delays in wealth growth but permanent damage to the path of compounding.

The article further warns that multiple current valuation metrics for US stocks are at historical highs: CAPE is near the 99th percentile since 1881, while the Buffett Indicator, Tobin's Q, and the equity risk premium also point to a similarly fragile environment. Meanwhile, the author refutes the traditional argument about "missing the best trading days," pointing out that most of the best single-day gains actually occur during bear markets and crisis phases, often adjacent to the worst trading days. For investment advisors and long-term investors, the issue is not predicting when the next crisis will arrive, but whether they can identify risks in advance through signals like valuation and market breadth, protecting compounding from damage before a long period of low returns arrives.

Below is the original text:

The traditional argument for stock investing is built on long-term average returns. But it doesn't fully consider what happens when a client's wealth accumulation phase happens to fall within the wrong 16 years.

Ryan Gorman, CFA, CMT, Shawn Keel, CFA, CMT, and Vincent Randazzo, CMT, portfolio managers at Tamarisk Capital Management and Quoin Capital Analytics, published a research paper via the CMT Association that every investment advisor should keep on their desk: "Navigating the Lost Decade: Protecting Long-Term Compounding in Secular Bear Markets." Based on 155 years of data from Robert Shiller's Yale University database, the paper presents an empirically solid and strategically urgent judgment: the so-called "lost decade" is not an anomaly but a structural characteristic of the stock market. And the current market environment shares similarities with the preludes to these historical phases, warranting serious attention.

The Historical Record Has Given a Clear Answer

The authors identify three distinct phases in the US stock market where buy-and-hold investors received virtually no real returns. From 1929 to 1954, it took the market 25 years to return to its previous real high. During the stagflation period from 1966 to 1982, the annualized real return was approximately -1.77% over 16 years. From 2000 to 2013, spanning the burst of the internet bubble and the global financial crisis, the annualized real return was about 0.05%, with a maximum drawdown of 52%. These three phases combined account for 54 years of market history, roughly 35% of the total time since 1871.

The authors state bluntly: "Lost decades do not need to be triggered by identical factors. They can occur in different economic cycles and institutional environments, but they provide investors with the same experience—prolonged drawdowns, impaired compounding, and negative behavioral reactions that often extend well beyond the market's eventual recovery."

International precedents further reinforce this judgment. Japan's Nikkei 225 index peaked at 39,000 points in December 1989 and did not reclaim this level until 2024, a span of 35 years. Europe's Euro Stoxx 50 index topped in March 2000 and only returned to its high at the end of 2025. The authors caution that the pattern of the US market always eventually recovering "should not be regarded as an unchangeable law."

The Mathematical Mechanism That Makes Losses Permanent

This is where the paper's analytical contribution goes beyond historical narrative. The authors demonstrate that a lost decade does not merely delay wealth accumulation; it causes permanent damage. Assume two portfolios both target a long-term average return of 7%, but one experiences a 13-year period of zero returns in the middle of its investment journey. The final terminal values will differ significantly. Path B ultimately achieves only 80% of Path A's terminal value. This gap is permanent and cannot be compensated for even if normal returns resume afterward.

The mathematical conditions required for recovery further amplify the problem. A 50% drawdown requires a 100% gain to break even. If the annualized return is only 3%—consistent with the returns available in historically high-valuation environments—breaking even takes 23.4 years. The authors clearly state: "This is the hidden cost of a lost decade: it brings not only the low returns of that period itself but also permanent damage to the compounding path."

Valuation Context: The 99th Percentile

The valuation section of the paper presents a finding that investment advisors should not overlook. The current CAPE (Cyclically Adjusted Price-to-Earnings ratio) stands at 39.9, placing it at the 99th percentile of all historical observations since 1881. Historically, only one instance has exceeded the current level: the peak of 44.2 in March 2000. The historical average CAPE is 17.7.

The authors are cautious in their wording—CAPE is not a timing tool—but its directional signal is very clear. When CAPE is in the lowest historical quintile, the average real return over the next 10 years is 10.7%, with no instances of negative returns. When CAPE is in the highest quintile, the average real return over the next 10 years is only 3.6%, with 24% of observations showing negative returns. The Buffett Indicator (total market capitalization to GDP ratio) is currently near 190%, higher than its peaks in 2000 and 2007. Tobin's Q and the equity risk premium also convey the same signal.

"When CAPE, market cap/GDP, Tobin's Q, and the equity risk premium all simultaneously indicate overvaluation, historical records show that the market's margin for error is narrowing."

Deconstructing the 'Don't Miss the Best Days' Argument

One of the most practical parts of the paper directly addresses a common industry argument used against tactical management. The authors examine the 20 best trading days for the S&P 500 between 1988 and 2025 and find that 18 of them, or 90%, occurred when the index was below its 200-day moving average. 42% of the best trading days occurred during traditionally defined bear markets.

This means: "The best trading days are not randomly distributed between bull and bear markets. They tend to cluster during crisis phases when prices are depressed." Furthermore, these best days during crises are often interspersed with the worst trading days. In October 2008, the market's largest single-day gain (+11.6%) occurred just days after its largest single-day loss. The two cannot be easily separated. The authors point out: "Investors cannot capture only the best trading days during these periods without also experiencing the worst ones."

A Framework for Market Breadth: What to Watch

The final section of the paper proposes a systematic framework for identifying market states, based on market breadth—observing the participation of different securities rather than relying solely on the average performance of a market-cap-weighted index. The core insight is that structural deterioration "often first appears in market breadth before it shows up in the market-cap-weighted price index."

Before the 1973-1974 bear market, the advance-decline line had already diverged from the S&P 500 in early 1973. In 1999, market breadth continuously deteriorated, preceding the tech stock crash of 2000. The authors argue that market breadth can provide "earlier warning signals than indicators based solely on price trends." When combined with the valuation context, this framework becomes even more explanatory: "High valuations set the backdrop... while deteriorating market breadth provides behavioral evidence."

Key Takeaways for Investment Advisors

The paper's conclusion is well-suited for client communication: "The question is not about choosing optimism or pessimism, but about choosing complacency or preparation."

Specifically, investment advisors should understand four points from this research. First, sequence-of-returns risk is not a theoretical concept. 35% of US market history has been in a "lost decade," and if a client retires during such a phase, they face not a temporary delay but permanent damage to compounding. Second, CAPE at the 99th percentile cannot predict a specific point in time, but it does define a more vulnerable market environment. Valuation and market breadth are not competing signals but complementary ones. Third, the "don't miss the best days" objection does not hold up to empirical scrutiny, as these best days are often concentrated in the same periods as the worst days; systematically managing drawdowns means avoiding both. Fourth, an adaptive framework prioritizing market breadth does not require precise market timing. It requires "a disciplined response to observable conditions, not a prediction of future outcomes."

The authors do not claim a fourth lost decade is inevitable. What history truly shows is that the conditions often present on the eve of a lost decade can be identified; and preparation always provides a more resilient foundation compared to passive acceptance.

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