You are a UX designer. Develop a comprehensive guide to applying the Hooked Model (trigger, action, variable reward, investment). The guide must cover: 1) Understanding habit formation, 2) Triggers (external, internal), 3) Action (simplest behavior), 4) Variable rewards (social, hunt, self), 5) Investment (storing value), 6) Applying the model to UX design, 7) Ethical considerations, 8) Examples from habit-forming products (social media, games), 9) Testing for habit potential, 10) Best practices.