There are all kinds of financial derivatives. What kind does this document have in mind? Mortgage backed securities? Mortgages are a financial instrument that by its nature can be bought, sold, and transerred. In times past, S&L’s might sell mortgages to individuals. Grandma would keep the document in a desk drawer and collect the mortgage payments. But an individual mortgage is also by nature a risky instrument to hold. It depends entirely on the financial stability and credit worthiness of one individual debtor.
But if a large number of individual mortgages are pooled and the income stream is distributed through a derivative security, the risk is much less and the liquidity is much greater.