Look up the meaning of "failures to deliver" in the stock market. In short: it means stocks sold by market makers and never delivered. AKA: they take your money when you buy a stock, it appears in your account, but they didn't actually deliver anything.
Then look up how many of those happen daily in any US stock.
Or read up here: Naked, Short and Greedy: Wall Street's Failure to Deliver by Susanne Trimbath