I invested in Gold as per Allens advice and when the big stock market crash occurred in 1987, I made a ton of money by being in other investments such as gold. Ditto for real estate that market plummeted inthe 80's. Following Allen's advice, I was able to pick up loads of real estate at bargain prices becuase most real estate investors back in those days saw real estate only as a tax benefit, not for gains. Their loss.
Multiple streams of Income covers this strategy. I highly recomend you read it if for that reason alone. Beats the typcial buy and hold (or is that buy and hope), dollar cost averaging and other so called sensible stategies which don't work unless you have a 20-30 year time horizon. Ask anyone who saw their investments plumet during the Jimmy Carter years back in the 70's how long they had to wait to get their investments back up to break even level. Want to take a guess? Would you believe 15 years? That is close.
For a person working for a wage, their source of income is their job, or their labor (aka their time that they sell to someone). But you can own a house, and rent it out, and when your renters pay you renter every month, the source of that income check is your rental property, or your house. It would just be called rental income. If you have money in the bank in an account that pays interest, those interest payments are another source of income. We can say the source is interest payments, or we can identify the asset that is generating rent, and say your money in the bank that is generating “rent” (aka interest) is your source of income.