As I understand it, there are 3 main phases of a business expansion.
The first happens after A recission and capital goods are bought with current resources.
The second happens after a while when capital goods are bought on credit where current income covers the payment.
The third happens when capital goods are bought on speculation that the buyer cannot pay the payment in whole and depends on a greater fool to buy it yielding a profit.
Then things to go hell, buyers go away, sellers have to sell at a loss or bankrupt.
Market crashes and liquidity drys up because banks are not sure of getting paid. Normal companies cannot meet payroll or buy raw materials because the banks are not lending and thing grind to a halt.
The fed will lend money to banks to kick start them, buy government securities at a discount from whoever putting cash into the economy. The sellers get a hair cut as an object lesson. And things get off zero. Cash gets into the system, payrolls get paid, raw materials get bought and yes folks buy stocks which slows or stops the crash.