Chapter 28: Quiz
1. The "21 days to form a habit" claim comes from: - A) A rigorous study on habit formation - B) Maxwell Maltz's observation about post-surgical adjustment, not habit formation - C) Lally et al. (2010) - D) James Clear's research
Answer: B. Maltz was a plastic surgeon observing adjustment to new appearance. The figure was never about habit formation.
2. Lally et al. (2010) found that habits take approximately: - A) 7 days - B) 21 days - C) 18–254 days (median 66) depending on complexity - D) Exactly 30 days
Answer: C. The range was enormous (18–254 days), with a median of 66. Simple habits formed faster; complex habits took much longer.
3. Implementation intentions ("if X, then Y") have a meta-analytic effect size of: - A) d = 0.05 (tiny) - B) d = 0.20 (small) - C) d = 0.65 (medium-to-large) - D) d = 1.50 (enormous)
Answer: C. Implementation intentions are one of the most well-supported behavior change techniques, with a medium-to-large effect size.
4. James Clear's emphasis on environmental design is supported because: - A) Willpower is a limitless resource - B) Stimulus control (making good choices easy) has strong evidence while ego depletion (willpower as a limited resource) has failed to replicate - C) The environment doesn't matter - D) Only celebrities can change their environments
Answer: B. Environmental design works; willpower management rests on a collapsed model.
5. Clear's "1% daily improvement compounds to 37x over a year" is: - A) A rigorous scientific finding - B) Mathematically correct but unrealistic for human behavior, which doesn't compound like interest - C) The basis of all habit research - D) Proven by longitudinal studies
Answer: B. The math works; the application to human behavior doesn't. Improvement plateaus, has diminishing returns, and isn't steady.
6. Lally et al. found that missing a single day of a new habit: - A) Completely reset the habit formation process - B) Did not significantly affect the trajectory of habit formation - C) Made the habit impossible to form - D) Required starting over from day one
Answer: B. Missing one day didn't derail habit formation — contradicting the popular "don't break the chain" advice.
7. The "cue → routine → reward" model from Duhigg is: - A) A complete and accurate model of all habitual behavior - B) A useful simplification that captures the role of environmental cues but oversimplifies the neuroscience of reward - C) Debunked by modern neuroscience - D) Only applicable to food habits
Answer: B. The model is useful as a practical framework but oversimplifies how reward actually works in the brain and doesn't capture all types of habitual behavior.
8. Which of the following is NOT an evidence-based behavior change strategy? - A) Implementation intentions - B) Self-monitoring (tracking behavior) - C) The 21-day rule - D) Environmental design
Answer: C. The 21-day rule has no evidence base. The other three are well-supported behavior change techniques.
9. Context stability (same time, same place, same preceding action) matters for habit formation because: - A) Habits form through cue-response associations, and consistent contexts strengthen these associations - B) Context has been shown to have no effect - C) Only morning habits work - D) Stability reduces creativity
Answer: A. Lally et al. found that performing a behavior in a consistent context accelerated automaticity — consistent with associative learning theory.
10. The chapter's overall message about habit formation is: - A) Habits are impossible to change - B) It takes exactly 21 days - C) Habit formation is real but slower, more variable, and more complex than pop psychology claims — evidence-based strategies (implementation intentions, environmental design, context stability) outperform willpower-based approaches - D) Only one strategy works for everyone
Answer: C. The evidence supports specific, practical strategies — but the timeline is longer than claimed, the process is more variable, and willpower-based approaches are less effective than environment-based ones.