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

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.

Brainstorm new interfaces that could introduce opportunities or threats to your business.

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

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.

The ultimate goal of a habit-forming product is to solve the user's pain by creating an association so that the user identifies the company's product or service as the source of relief.

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.