I’m somewhat embarassingly reminded of Harry Potter and the concept of “Horcruxes” here, in that the goal is to find a piece of your value, and impart it into an inanimate object or product, Voldemort Style (did I really just make a Harry Potter reference?) Anyways, whatever. If you want passive income, you have to think about the value you rent out or own. Or, you need to buy something valuable that other people would like to use (I love the idea of a 3D Printer). Then put it into something that can be sold or rented more passively. Maybe you have a car that sits in the driveway, or a vacation home that is empty half the time. Maybe you just have some funny jokes you could put into a YouTube video and run ads on. At some point, you have to “transfer” the value into something that can work for you — that something is an asset.
There are a few advantages to taking this approach. First, you get close to 100% of your listed price (minus the transaction fee of your preferred payment gateway). Second, you are not competing with other authors and have the reader’s attention solely on your product. Third, selling your eBook on your own platform is a great opportunity to build a long term relationship with your readers via email. Fourth, you can bundle your eBook with other goodies in order to bump up the value and make it more unique. With so many advantages, it's worth putting up the time and start building your own platform.
While it is important to find something that you love to do and turn it into a money making business, you do have to be cognizant of the return as you pointed out. There are many opportunities that I found and tried out that at the time seemed great. But when I took a step back, I realized that I was working a lot for very little income whereas other things I love doing brought in much more money.
Creating passive income is the key to retiring, especially retiring early. If you want to retire early with the stock market you will have to save a huge amount of money, because that money has to last so long and retirement calculators depend on you using your investment to fund your life. With passive income you will have income coming in as long as you own the investment, without every eating away at the principle invested. Creating passive income may take more work than investing in the stock market, but I think it is well worth the extra effort!