Some say that one important factor in the rise and fall of stock markets is the FED's balance sheet. Stocks tend to rise with QE (Quantitative easing) and fall with QT (Quantitative tightening).

This link gives a good idea of the impact of QE and QT : St. Louis Fed (FRED): (Assets: Total Assets: Total Assets (Less Eliminations from Consolidation): Wednesday Level - Liabilities and Capital: Liabilities: Deposits with F.R. Banks, Ot (that formula is borrowed from someone on Twitter, can't remember his name at the moment). There is a giant jump in 2020 and that matches the rise of stocks. The peak in Sept. 2021 was not far from the top of the market. Add the rise of the interest rates and that seems to explain the bear market.

If this relationship continues between the FED's balance sheet and the markets, then the following years could be bumpy as the FED said they wanted to reduce their balance sheet. But all we need is a recession for them restart QE...