You'll often find that people's declared preferences - what they say they want - are far different from their revealed preferences - what they actually do.
Nir EyalInstead of relying on expensive marketing, habit-forming companies link their services to the users' daily routines and emotions.
Nir EyalWhen designers intentionally trick users into inviting friends or blasting a message to their social networks, they may see some initial growth, but it comes at the expense of users' goodwill and trust. When people discover they've been duped, they vent their frustration and stop using the product.
Nir Eyal