$10K put into the S&P 500 in October 2006 grew to about $80.8K over the next 20 years. Miss its 10 best days and you'd have $35.9K. That's with dividends reinvested, from Oct 26, 2006 to present. → Stayed invested: $80.8K → Missed the 10 best days: $35.9K → Missed the 20 best days: $21.2K → Missed the 30 best days: $13.9K → Missed the 40 best days: $9.5K There were about 5,000 trading days in that stretch. Sitting out the best 40 of them, less than 1%, left you with less than the $10K you started with. All 10 of the best days came during the 2008-09 financial crisis, the 2020 Covid crash or the April 2025 tariff selloff. The biggest was Oct 13, 2008, when the index jumped 11.6%, two trading days after one of its worst drops.