A dark pattern is a user interface carefully crafted to trick users into doing things they might not otherwise do, such as buying insurance with their purchase or signing up for recurring bills. Normally when you think of “bad design,” you think of the creator as being sloppy or lazy — but without ill intent. Dark patterns, on the other hand, are not mistakes. They’re carefully crafted with a solid understanding of human psychology, and they do not have the user’s interests in mind.
The thing about dark patterns is that you design them from the exact same rulebooks that we use to enhance usability.