A buyer requires a seller there can be no “sidelines

For every buyer, there must be someone willing to sell. As noted by Clifford Asness:

“There are no sidelines. Those saying this seem to envision a seller of stocks moving money to cash and awaiting a chance to return. But they always ignore that this seller sold to somebody, who presumably moved a precisely equal amount of cash off the sidelines.”

Every transaction in the market requires both a buyer and a seller, with the only differentiating factor being at what price the transaction occurs. Since this is necessary for there to be equilibrium in the markets, there can be no “sidelines.” 

MarketWatch 5 January 2021

https://www.marketwatch.com/story/investors-are-waiting-for-cash-on-the-sidelines-to-juice-the-stock-market-this-is-why-that-idea-is-hogwash-11609795905