Behavioral economics describes consumer lock in as ”the decreased likelihood to search for other options, or change to another option, once an investment in something has been made. The initial investment, called a setup cost, can be big or small.”
This same concept can transfer to UX, in something that can be described as engagement lock in. Engagement lock in is about finding ways to retain the user through a given flow, by crafting the experience such that there is a perceived setup cost. This can be achieved through the use of progressive disclosure, progress feedback, hints of completion rewards, etc. This isn’t some arbitrary evil exercise – UX has the very difficult task of crafting an experience that both facilitates users in starting a new flow, while easing and motivating them through the flow’s completion. Some of these flows can be very complex and require a high level of engagement; crafting flows such as these requires a lot of intentionality.
Trickier still is the fact that the digital media of UX brings in new challenges; in this space, lock in is elusive and subtle, given that setup costs are often transient and disposable. These costs are measured in fractions of a second, having gone from screen one to screen two, or the fact that your product is the one currently on screen (if only for a brief moment); any of these can easily be reversed by canceling out of an initiated action, or being interrupted by another app or service. Setup costs are brief and fragile, but they are there, and you cannot not design for them.