One of the things I'm surprised your article doesn't mention is the tax advantages of this type of investment. The depreciation and rehab costs (purchasing distressed properties) can be huge deductions to ones income taxes, which none of the others have. Then, along with the appreciation of real estate, this passive income investment outperforms the notion of maxing out my 401k as well.
A perfect example of the Active Problem Solving + Automation concept is in my online courses I’ve created over the years, or my free webinars I’ve created more recently Each of my online courses and webinars are targeted to help people with specific problems, whether that’s in the area of affiliate marketing, podcasting, building a brand, and so forth. I am always improving upon the courses, but they are also evergreen for my audience.
How passive it really is: Excellent – Once your ads are running, you could literally just sit back and watch the money roll in.  Again, you are spending money to make money here, so there is risk involved.  However, once the ads are set, the income can be very passive.  Keep in mind, you may need to monitor and possibly modify ads if they aren’t performing well.

The craziest part of this was I’d wake up in the morning and there would be more money in my bank account, from people who had bought my book overnight. When you think about it, an online store that sells something that’s digital is something that’s open 24 hours a day, 7 days a week, 365 days a year. Using tools, software and systems, you can automate the delivery process so you literally don’t have to do anything to serve that audience. That’s super powerful.

Most of us think of investment income as just the cash flow we get from bank interest, bonds, share dividends and property rents, some of which comes via a super pension.  But a more complete view is to also consider how growing the value of your investments can add to your spending potential.  This total return approach generates income from both income and growth to optimise spending from your portfolio across all market cycles, aligning cheap and expensive investments to your goals.