2. Focus on income-producing assets. Internet growth stocks may be sexy, but they provide no income. To build a large enough passive-income stream to survive, you must invest in dividend-generating stocks, certificates of deposit, municipal bonds, government Treasury bonds, corporate bonds, and real estate. You're free to invest in non-income-producing assets for capital appreciation too. You just want to earn reliable income when the day comes to leave your job.
Think about it.  If you are saving for retirement, you are trying to save enough in investing to generate enough income to replace your primary salary.  Let’s take my friend’s example above: $50,000 a year.  To generate $50,000, you would need to have almost $1,700,000 saved, and be able to generate a 3% cash flow on that money (which is reasonable if invested in dividend paying stocks).

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.