06/05/2026
The Century-Old Chart Warning Us About Mean Reversion 📉
Looking back over the past century, ever since the 1929 Wall Street crash and the ensuing Great Depression, the S&P 500 has spent more than 99% of its time trading within a ±2 standard deviation (SD) range of its Logarithmic Regression Channel (see chart). Even on the eve of the 2000 Dot-com bubble peak, the index only managed to reach the +2 SD upper boundary before rolling over and entering a prolonged correction.
Currently, although the S&P 500 has not yet touched the top of the channel, it has entered the +1 to +2 SD zone. This indicates that price action is clearly overextended, and the gravitational pull of mean reversion is steadily accumulating. Naturally, accurately predicting the end of this rally is impossible, and there is no need to obsess over timing the exact market top. However, if this century-old macro trend remains valid, it suggests that the closer the index gets to the +2 SD ceiling, the higher the risk of triggering a significant mean reversion.
Based on current channel projections, the ultimate peak of this bull cycle could occur anywhere between current levels and approximately 8,800 points. In other words, while the market may not have confirmed a top just yet, the risk-reward scale is gradually tipping in an unfavorable direction.
For investors, we may have passed the point of asking, "How much higher can this go?" It is now time to evaluate a more pressing risk: "Once mean reversion occurs, how steep could the pullback be?"