This is the secret to financial freedom, but is unfortunately not well understood
Dividend income and rental income are perhaps the classic two, and now you can add to that additional income streams from delegating Steem power, staking PoS coins, renting out EOS (in future), running a couple of smart nodes etc
Compounding of dividends and rental income is pretty slow, but if you can replicate the process with assets growing as rapidly as STEEM has done recently, then you turbo charge the process to a life-changing degree
Cheers