An example of this is the sale of a mutual fund. While the majority of the income is taken by the broker up front, there are small trails of income associated with them. Another job that has components of passive income are insurance sales. Whether disability insurance, life insurance, or health insurance, there are varying levels of passive income that get paid to the agent for years into the future.
This just goes to show that not only should you strive to produce products that deliver income long after you build them, but you can also look for passive income in your career. This can result in benefits long into your future, as you may move on to another job or career, but still receive payments on work done 10 years prior.
Good night and good luck.
I am a Chicago-area financial adviser to young doctors & business owners.