[edmundsauto]

The most important line in finance is "Past performance is no guarantee of future results". This is generally treated as a warning label: Don't assume an investment will continue to do well in the future simply because it's done well in the past.

However, what it really means is that nobody can predict future performance, even with historical data. I think it's negativity bias that this phrase is used to apply to downside; it should also be used when considering upside. (The reason, I think, is many people prefer to miss out on upside rather than experience downside, ie we are risk-averse.)

Over some future time frame, the S&P will go up again. It doesn't feel like that will be soon, but as I always admit to myself: I am really bad at predicting the future.