To save time and effort, a person can group two or more of their passive activities into one larger activity, provided they form an "appropriate economic unit," according to Publication 925 - Passive Activity and At-Risk Rules. When a taxpayer does this, instead of having to provide material participation in multiple activities, they only have to provide it for the activity as a whole. In addition, if a person includes multiple activities into one group and has to dispose of one of those activities, they’ve only done away with part of a larger activity as opposed to all of a smaller one.
Cost per action/sale methods require that referred visitors do more than visit the advertiser's website before the affiliate receives a commission. The advertiser must convert that visitor first. It is in the best interest of the affiliate to send the most closely targeted traffic to the advertiser as possible to increase the chance of a conversion. The risk and loss are shared between the affiliate and the advertiser.
The doctor or lawyer, for instance, could use her or his income to invest in a medical start-up or buy shares of medical companies he understands such as Johnson & Johnson. Over time, the nature of compounding, dollar cost averaging, and reinvesting dividends can result in her or his portfolio generating substantial passive income. The downside is that it can take decades to achieve enough to truly improve your standard of living. However, it is still the surest path to wealth based on the historical performance of business ownership and stocks.