If users are not doing what the designer intended (when users are investing time, effort, etc in your product), the designer may be asking them to do too much.

As fleeting commitments, diets often fail. Thinking of dietary choices as part of who you are...can give them real staying power

Habit-forming products alleviate users' pain by relieving a pronounced itch.

User habits are a competitive advantage. Products that change customer routines are less susceptible to attacks from other companies.

Like flossing, frequent engagement with a product, especially over a short period of time, increases the likelihood of forming new routines.

Fogg states that all humans are motivated to seek pleasure and avoid pain; to seek hope and avoid fear; and finally, to seek social acceptance and avoid rejection

When 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.