Another way to generate passive income is to invest and be a silent partner in a business. This is very risky, but with risk comes the potential for high returns. For example, several years ago both Lyft and Uber were looking for private investors to invest in their companies. Today, they are worth billions - but you as an investor would only reap that benefit if they go public via an IPO, or get acquired. So, it's risky.
According to Uncle Sam, you need to be "materially involved" in an enterprise to earn active income. With passive income, it's just the opposite, as the IRS deems you to be earning passive income if you're not materially involved with a profit-making enterprise. By and large, expect income to be taxable if you are engaged in a passive income enterprise. You will need to report earnings to the IRS. 

If an investor puts $500,000 into a candy store with the agreement that the owners would pay the investor a percentage of earnings, that would be considered passive income as long as the investor does not participate in the operation of the business in any meaningful way other than placing the investment. The IRS states, however, that if the investor did help manage the company with the owners, the investor's income could be seen as active since the investor provided "material participation." 
​Affiliate marketing is the practice of partnering with a company (becoming their affiliate) to receive a commission on a product. This method of generating income works the best for those with blogs and websites. Even then, it takes a long time to build up before it becomes passive. If you want to get started with affiliate marketing check out this great list of affiliate marketing programs.
Skillshare is more of a social learning platform where you can teach real-world skills. The range of skills that you can teach is only limited by your imagination - from board game strategies, garment construction, cooking tutorials, travel hacking, and relationship tips. I even saw a course on how to build a grown man's wardrobe. Creating a class on Skillshare is free. For each student who enrolls, Skillshare takes a 30% fee (Similar to Udemy). You are also provided a unique teacher referral link that lowers the fee to 15% for students who enroll via your referral. Note that all online courses on Skillshare go through an approval process based on specific criteria.
If you can max out your 401k or max out your IRA and then save an additional 20%+ of your after-tax, after-retirement contribution, good things really start to happen. If one is looking for earlier financial independence, such as retiring in their 40s or early 50s, it may be a good idea to skew towards more after-tax savings and investments given one has to wait until 59.5 to withdraw from their 401k or IRA penalty-free.
If someone stole my hard work and passed it off as their own, I’d be livid and would pursue them to the ends of the Earth for full restitution. A man I hired to work with me registered my preferred domain name of my business and has re-registered it in subsequent years. That’s bad enough; I’m mad as hell. The worst aspect of his behaviour is that I don’t know WHY he has done that; I paid him the fee we had agreed on and thanked him for his input. We also got along perfectly well during the project so far as I know, so I don’t see what his problem is.

This is the basic mistake they've made: they've fallen prey to the belief that money and meaning are two totally separate things. They've chosen to make their money from something that feels completely meaningless to them (some business they care so little about, they just can't wait to get away from it and minimize their involvement as much as possible), which they hope will buy them the freedom to do something they actually care about.
* I use Personal Capital to track all my finances in one place. It’s much easier to use their free software to follow 28 accounts on one platform than to log into various accounts to check my balances. They’ve also got great tools for x-raying your portfolio for excessive fees, recommending a more optimized asset allocation, and planning for retirement with their Retirement Planner.