With passive income sources, you can go long periods of time without doing work, yet still earn income. In some cases, that income can expand without much additional input from you. For example, if I build a website in 5 hours and after a month, it has only made $50, my time to that point was worth $10/hour. It doesn’t stop there, however. In a year, if the site has earned $600, the value of those initial 5 hours grows to $120/hour. As time goes on, that number can continue to grow indefinitely.
How do you do this?  Well, try to get the highest paying job you can!  Ask for a raise!  Utilize services, such as Glassdoor.com, to see how your salary competes with others in your same job.  Some companies really force employees to leave to get a raise, and then come back for another raise.   This industry jumping promotional strategy is very common and could work.
Reality Two: You have a limited amount of time on this planet to implement your business plans and strategies, while also trying to balance the needs of family, health, spirituality, recreation, relationships, and much more. Do you really want to spend your limited time nursing more than one stream of income? Happiness has more to do with balancing life than making tons of money.

What I Do: I’ve set up multiple investment accounts outside my main operations bank that deals with working capital e.g checking, paying bills. By transferring my money to a couple brokerage accounts and two other banks as soon as it hits my main bank I no longer have temptation to spend on frivolous things. As a result, I can wake up 10 years later and reap the rewards of compounding. My 401(k) is the best example where constant contributions over 18 years has grown to over $500,000 without any savings pain given it just became a part of life. Real estate is also a fantastic asset class for the long term. It’s fantastic to enjoy your home, pay down your mortgage each month, and end up with a paid off asset that has likely appreciated during your time of ownership. 

But two months later, with the economy slowing down after the financial crisis, his firm began laying people off, and Flynn was informed that after his current projects were finished, he also would be out of a job. At the same time, he couldn’t help but notice that in the LEED exam forums he had frequented, people were referring to him as an expert and directing questions his way. He began to think he might capitalize on that.
Vanguard: Vanguard has a minimum of $50,000 and a fee of 0.3%. Rebalancing is done automatically once every quarter and tax loss harvesting is done on a client-by-client basis. We included Vanguard because clients who invest between $50,000-$500,000 have access to a team of financial advisors. Those with accounts over $500,000 will have a dedicated advisor.
I agree that it is important to establish multiple sources of income, but I would be hesitant to group dividend stocks and real estate into the “multiple streams” bucket. Those are investments, and living off of investment income because you are in an emergency state is not a good plan. Cash flow from investments ebbs and flows more than the cash flow from a day job.
ie first you need to haul ass and do something crazy, eg write a quality 20,000 word ebook (insanely not passive hahahah), but then you get to sit back and enjoy seeing PayPal sale messages pop up on your iPhone each morning as sale after sale after sale is made…on an ongoing basis and without any additional work. That’s some seriously Pina Colada flavored passive goodness!
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The theoretical generalization to more than one period is a multi-period wealth and income constraint. For example, the same person can gain more productive skills or acquire more productive income-earning assets to earn a higher income. In the multi-period case, something might also happen to the economy beyond the control of the individual to reduce (or increase) the flow of income. Changing measured income and its relation to consumption over time might be modeled accordingly, such as in the permanent income hypothesis.
In January 2018, I missed my chance of raising the rent on my new incoming tenants because it didn't come to mind until very late in the interview process. I didn't write about my previous tenant's sudden decision to move out in December 2017 after 1.5 years, because they provided a relatively seamless transition by introducing their longtime friends to replace them. I didn't miss a month of rent and didn't have to do any marketing, so I felt I'd just keep the rent the same.
Buy a small business: A local small business, like a car wash or a laundromat, is a great way to put money down on a money-making venture. Automate it so you don't have to be on the premises unless you're collecting money. Go into a local business with your eyes wide open - study the books, especially on income and expenses, and examine water and utility bills if your venture will be open 24 hours.

However, under certain circumstances, payment for personal services performed in the United States is not considered income from sources within the United States. For example, personal services performed by an independent nonresident alien contractor specifically exempted by a tax treaty. For more examples, see the Pay for Personal Service section in Publication 515, Withholding of Tax on Nonresident Aliens and Foreign Entities.