Charles Schwab economists are drawing parallels between current market conditions and those of 2021, warning of a potential bear market due to the growing disparity between individual stock performance and index levels like the S&P 500. While tech stocks have surged, the majority in these indexes do not reflect such gains, raising concerns. The S&P and Nasdaq are experiencing declines in the number of stocks trading above their 50-day moving average, reminiscent of pre-bear market signals in 2021. There is a notable concentration in a few key stocks, like Microsoft, Nvidia, and Apple, which collectively account for over 20% of the S&P's value, posing risks to market stability and investor portfolios.