Writing an e-book is very popular among bloggers, as many have noted that “it's just a bunch of blog posts put together!” You will not only have to make an investment of time and energy to create the e-book, but market it correctly. However, if marketed correctly (through blogging affiliates in your niche, for example), you could have residual sales that last a very long time.

Many people talk about passive income and create the impression that you never have to do anything to keep that income going. The truth is that you will normally have to keep your eye on things if you want it to run smoothly. For example Richard Branson doesn’t run any of the 400+ companies he started but he goes over the numbers each day to make sure they’re performing well and calls the CEO if there are any problems.
Managerial accounting defines residual income in a corporate setting as the amount of leftover operating profit after all costs of capital used to generate the revenues have been paid. It is also considered the company's net operating income or the amount of profit that exceed its required rate of return. Residual income is normally used to assess the performance of a capital investment, team, department or business unit.