複数の研究で証明された「暴落はバーゲンだ！買い増し！」というのが全く賢くない理由を解説します。

Main takeaway

The video argues that holding cash for a market crash and then “buying the dip” is not reliably better than investing regularly or investing available funds promptly. Across the studies discussed, dip-buying often produced lower returns, with results depending on how long investors waited and how much cash they kept aside.

The discussion is aimed at long-term investors in diversified index funds. The presenters explicitly say it does not address individual stocks or high-dividend stocks.

Research and evidence discussed

• 75-year daily-data simulation: Compared investing $20 per day with a dip-buying rule that invested accumulated cash after the market fell more than 2% from its level 22 trading days earlier.

  • Dollar-cost averaging (DCA) ended at about $20.246 million, versus $19.8 million for dip-buying.
  • A more complex momentum approach—buying only when prices were trending upward—ended at about $20.255 million, close to DCA.
  • The video’s point: extra timing effort did not produce a meaningful advantage in this comparison.

• Javier Estrada, IESE Business School — “Buy the Dip? Not So Fast”: As cited in the video, this study used data from 1871–2025 to examine 30-year investment periods, including the S&P 500 and 10-year U.S. Treasury bonds.

  • It compared 100% stocks with a strategy starting at 60% stocks / 40% bonds, then shifting 25% of the bonds into stocks during monthly declines.
  • Dip-buying had an annualized return about 0.2 percentage points lower and a final value about 5% lower than buy-and-hold.
  • Its reported volatility was about 0.4 percentage points lower and its maximum decline about 2.1 percentage points smaller, but its Sharpe ratio was worse.
  • Waiting for larger declines—3%, 6%, 9%, 12%, or 15%—generally meant waiting longer and receiving lower returns. A larger allocation to reserves also weakened returns and the Sharpe ratio.
  • In a cash-reserve illustration, 100% stocks returned 9.4% annually and grew to $1,965 over 30 years, compared with 6.0% and $569 for a dip-buying strategy holding 40% in non-interest-bearing cash. These are study results as presented in the video, not forecasts.

• Nick Maggiulli, Just Keep Buying: A roughly 1920–2018 U.S. market analysis compared monthly investing of $100 over 40-year periods with attempts to wait and invest accumulated cash at market lows.

  • DCA reportedly beat an investor who could identify and buy the exact bottom in more than 70% of the comparisons.
  • Against a less-than-perfect timer who bought about two months after the bottom, DCA reportedly won 97% of the comparisons.
  • The video uses this to illustrate how difficult it is to time downturns consistently.

• Value averaging: Proposed by Harvard professor Edleson in 1988, this approach sets a rising target portfolio value. Investors contribute more when the portfolio is below target and reduce contributions or sell when it is above target.

  • A 2000 paper by Paul S. Marshall and others argued, using Monte Carlo simulations, that value averaging could improve average purchase price and internal rate of return versus DCA.
  • The video cites papers by financial scholar Simon Hayley (2013 and 2014) that challenge that conclusion. It argues that value averaging can make the internal rate of return look high partly because it changes when money is invested and withdrawn.
  • In a rising market such as the S&P 500, value averaging may leave more cash uninvested and produce a lower final portfolio value than DCA. Its apparent advantages may depend on assumptions such as volatile, sideways markets or access to unlimited additional funds.

• PWL Capital, six-country comparison: This analysis covered 10-year investment periods, using U.S. data from 1926–2020 and data for Canada, Germany, Japan, the U.K., and Australia from 1970–2020.

  • It compared investing a lump sum immediately with waiting for a 10% or 20% decline before investing; the dip strategy held funds in U.S. Treasury securities while waiting.
  • The reported average annual return from immediate lump-sum investment was higher in all six markets. Returns generally fell as the decline threshold—and therefore the wait—increased.
  • The study also examined market highs. As presented in the video, a high followed by a decline of at least 10% within 12 months was uncommon; the figure cited was under 3% overall and 1.14% for the U.S. The video’s broader point is that new highs occur regularly and do not automatically mean investors should wait for a pullback.

• Schwab Center for Financial Research illustration: Five hypothetical investors each had $2,000 per year to invest over 20 years through 2024: an ideal investor buying at annual lows, an investor making an annual lump-sum investment, a monthly investor, an unlucky investor buying at annual highs, and a cash-only investor.

  • The ideal timer came first, but even the unlucky investor buying at highs ended with far more than the cash-only investor.
  • The video emphasizes that continuing to invest and avoiding panic-selling matter more than achieving perfect timing.

Practical framework and cautions

• For long-term index investing, the video favors following a regular investment plan and investing when money is available, rather than waiting for a crash.
• Buying more during a downturn is only feasible if genuinely surplus money is available. Successfully reserving and deploying it around the bottom is not a dependable skill.
• Keeping some cash can still be reasonable for financial security and peace of mind, even if holding it specifically to time a dip may reduce expected returns.
• The overall message is not to panic during declines, sell investments impulsively, or feel compelled to buy extra just because prices are described as “on sale.”
• No explicit “not financial advice” disclaimer appears in the subtitles.

Assets and instruments mentioned

• Equities and index funds, including the S&P 500
• Bonds, including 10-year U.S. Treasury bonds
• U.S. Treasury securities held while waiting to invest
• Cash
• No individual stock tickers, sectors, or cryptocurrencies are discussed.

Presenters and sources

Presenters and voices include the channel’s 節約ちゃん (Setsuyaku-chan) and 貯金ちゃん (Chokin-chan). The video metadata also credits an おふとんP voice for the creator/narrator role.

Research and sources named include Javier Estrada / IESE Business School, Nick Maggiulli, Just Keep Buying, Edleson, Paul S. Marshall and co-authors, Simon Hayley, PWL Capital, and the Schwab Center for Financial Research.