Think of at least three conventional ways to trigger your user with current technology (emails, notifications, text messages, etc.). Then stretch yourself to come up with at least three crazy, or currently impossible, ideas for ways to trigger your user (wearable computers, biometric sensors, carrier pigeons, etc.).

You may find that your crazy ideas spur some new approaches, which may not be so crazy after all. In a few years, new technologies will create all sorts of currently unimaginable triggering opportunities.

— Hooked: How to Build Habit-Forming Products by Nir Eyal, Ryan Hoover