Chapter 28: Exercises

Comprehension Check

1. Where does the "21 days to form a habit" claim actually come from? Why is it wrong? 2. What did Lally et al. (2010) find about the time to habit formation? What factors affected the timeline? 3. What does James Clear get right in Atomic Habits? Where does he oversimplify? 4. Explain implementation intentions. What is the meta-analytic effect size? 5. Why is environmental design more evidence-based than "willpower management"?

Application

6. Choose a small behavior you want to make habitual. Use implementation intentions: "After [existing habit], I will [new behavior] for [2 minutes]." Track it for 30 days. Note how long it takes to feel automatic. 7. Apply environmental design to one behavior: make a desired behavior easier (remove friction) and an undesired behavior harder (add friction). Document what you changed and the effect. 8. Apply the toolkit to: "Build one keystone habit and everything else will follow." 9. Compare Atomic Habits and The Power of Habit to the evidence-based strategies listed in this chapter. Which recommendations are supported? Which are unsupported? 10. Track a habit you already have. Identify the cue, the behavior, and what happens after. Does the cue → routine → reward model fit?

Critical Thinking

11. Clear's "1% daily improvement" math is correct but the premise (steady compound improvement in human behavior) is unrealistic. Is this type of motivational math helpful or misleading? 12. Lally found that missing a single day didn't significantly affect habit formation. Why might this finding be more important than the 21-day or 66-day numbers? 13. Atomic Habits has sold 15 million copies. Does commercial success validate the advice? (Apply Chapter 5's analysis.) 14. Why has implementation intentions (d = 0.65) not gone viral the way "21 days" or "atomic habits" have? 15. If context stability matters most for habit formation, what does this imply for people with unpredictable schedules (shift workers, parents of young children)?

Fact-Check Portfolio

16. If any of your 10 claims involve habits, routines, or behavior change: - Check for the 21-day myth - Identify whether evidence-based strategies are being used - Update your evidence rating.