The thesis
“Just buy the S&P 500 index fund and never look at it again.”
How buffet read it
$10,000 invested in SPY, the S&P 500 ETF.
Ten years: 2016–2026.
Dividends reinvested, no rebalancing, no trading.
Benchmark: S&P 500.
SPY · 2,513 trading days · benchmark SPY
$10,000 became
$0
This thesis is the S&P 500, so it returned what the index returned over 2016–2026: $41,459. There is no gap to explain — the question is whether you would have sat through the fall below.
The worst stretch
−33.7%, February 2020 to March 2020 — you would have sat through one month of that, and it took until August 2020 to get back to level.
the S&P 500 fell 33.7% at its worst over the same period. The thesis moved 18.0% a year against 18.0% for the index.
Where the thesis was wrong
SPY returned +314.6% from 2016 to 2026, which is exactly what the S&P 500 returned, because SPY is the S&P 500. Holding it required sitting through a −33.7% drop between February 19 and March 23, 2020, with no recovery until August 10, 2020. In 2022 the position fell −18.2%, and in 2018 it gave back −4.6%, both years ending lower than they started. The thesis asked for no looking; the drawdowns tested whether that was actually possible.
Counter-test
Same money, same schedule, parked in 1–3 month T-bills instead: $12,510.
Year by year
| Year | The thesis | SPY |
|---|---|---|
| 2016 | +3.7% | +3.7% |
| 2017 | +21.7% | +21.7% |
| 2018 | −4.6% | −4.6% |
| 2019 | +31.2% | +31.2% |
| 2020 | +18.4% | +18.4% |
| 2021 | +28.7% | +28.7% |
| 2022 | −18.2% | −18.2% |
| 2023 | +26.2% | +26.2% |
| 2024 | +24.9% | +24.9% |
| 2025 | +17.7% | +17.7% |
| 2026 | +13.4% | +13.4% |
What this verdict does not include
- US-listed stocks and ETFs only, priced on end-of-day closes.
- No tax, no trading fees, no slippage, no bid-ask spread.
- Dividends are reinvested, because closes are adjusted for them.
- Survivorship is not corrected for: only instruments that exist today are held.
- Only 10 years of history exist for this. Read it accordingly.
- Single-leg, buy-and-hold — exactly as the thesis describes.
- Benchmark is the same instrument; this run shows the raw growth of the strategy itself.
Keep this thesis
buffet re-runs it once a month and mails you the new number. Nothing else is ever sent.
Another thesis
Every verdict names something it could not test. That gap is usually the next thesis.
Run another thesis — $5