Depending on specialty, most of us can expect to be involved with a malpractice suit at least once in our career.  But what if you had 3 cases in the same year?  It is likely that you wouldn’t be able to continue to get malpractice coverage.  Or, if your malpractice is through a group, the insurance company may insist you be thrown out of the group or else the whole group’s rates will go up.  I know of at least one doc who was recently let go partly at the insistence of the malpractice insurance company.  Think your disability policy will cover this?  Think again.

Real Estate Income – Since we moved up to Newport Beach, I started renting out my condo in San Diego. My monthly cash on cash return is $300(I charge $1,900 for rent and my total payments including mortgage, HOA, property tax and insurance are $1,600) but I also get back around $350 every month in principal and about a $150 tax savings per month. But even this income is inconsistent, since sometimes expenses will pop up like last month when I had to buy a new A/C for $3,000!

The one thing I learned though from all those childhood experiences though is that you never can depend on one source of income. Eventually my mom caught on and stopped giving me all those extra bags of chips and I had to figure out a new way to make money. No matter how safe something seems there’s always the chance that you could lose that income and be stuck with nothing.
One of the earliest ideas on the circular flow was explained in the work of 18th century Irish-French economist Richard Cantillon,[2] who was influenced by prior economists, especially William Petty.[6] Cantillon described the concept in his 1730 Essay on the Nature of Trade in General, in chapter 11, entitled "The Par or Relation between the Value of Land and Labor" to chapter 13, entitled "The Circulation and Exchange of Goods and Merchandise, as well as their Production, are Carried On in Europe by Entrepreneurs, and at a Risk." Thornton eds. (2010) further explained:

This is a venture that is growing rapidly. You can create videos in just about any area that you like — music, tutorials, opinions, comedy, movie reviews — anything you want . . . then put them on YouTube. You can then attach Google AdSense to the videos, which will overlay your videos with automatic ads. When viewers click on those ads, you will earn money from AdSense.
eBay Store: It’s now easier than ever to run an online eBay store. You can, of course, acquire products to resell on eBay. But you can also create an online store to market products that others are selling on eBay and share in the commissions generated by the sales. Recently I interviewed a family friend who started her own eBay store and now makes five figures from home. Check out the interview here.
My advice is that you use some sort of marketing (Facebook Ads, PPC, Instagram stories, etc) to keep your sales growing and healthy. Also there is a free extension called "Keywords Everywhere" and it gives you the exact amount of search volume certain keywords have so I definitely recommend you check that out on Chrome Web Store it's pretty accurate. In order to win you need to stand out with your product: so pick a color and or new feature by contacting your supplier and modifying something to your product so you aren't selling the exact same product everyone else is. This will easily help you make more impressions and sales just with that alone. Slapping your own powerful logo on your product (Tip: Don’t worry, it’s extremely easy to do this, you can outsource a logo for like $5 on Fiverr) is going to make you look like a very professional and credible seller giving you access to 1000’s of sales in a month. Amazon isn’t a gimmick, get started now and don't wait! I have a complete guide for beginners explaining everything simply and giving my personal tips for you to grow your own business. You can rank your product on page 1 pretty easy and doing so will make your product viewed by hundreds of thousands of purchase ready customers. I strongly recommend if you're picking a product on Amazon to sell that you make sure it has steady search volume and has actual demand. You can't sell any product if no one is searching for it (No demand). (TIP: you can use google keyword planner / trends to see products that are trending.) Amazon isn’t a gimmick, get started now and don't wait! It's not saturated despite what people say. This takes work, so if you're willing to work at this then this will replace full time income. If you have any questions feel free to ask, I am a wealth of information on this topic. Anyone who isn’t jumping on this opportunity is losing out. You need to get started as soon as possible.

To create residual income, you need to create something that people will continue to buy on a regular basis long after you’ve created it. A house is a prime example of this as people will continue to pay rent for the right to live in the house. A business needs to have products that are sold over and over again rather than trading the business owner’s time for money.