What does it mean that default replacement strategy?

Replace an unproductive default with a specific productive alternative.

Example: A marketing manager notices she has six unproductive defaults running simultaneously: she checks Instagram when stressed, snacks on candy when bored, opens news tabs when stuck on a problem, scrolls LinkedIn when waiting for a meeting, sits motionless for hours between scheduled walks, and watches TV until exhaustion replaces sleep. She tries to fix all six at once and lasts three days before reverting entirely. On the second attempt, she picks one — the stress-triggered Instagram check — and designs a single replacement: when she feels the stress impulse, she opens a notes app and writes three sentences about what is bothering her. Same cue, same brief escape from the task, but the new routine produces clarity instead of distraction. After eighteen days, the replacement holds without effort. She moves to the next default. Within four months, she has replaced five of six. The sixth — the TV-until-exhaustion pattern — collapsed on its own once the stress default stopped feeding it anxious energy at bedtime.

Try this: Choose one default you identified in earlier lessons (productive, healthy, social, stress, boredom, or phone-checking). Write the full replacement specification: (1) the trigger that activates it, (2) the reward it currently delivers, (3) your replacement behavior that responds to the same trigger and delivers a comparable reward, (4) one friction reduction you will make to the replacement, and (5) one friction increase you will add to the old default. Implement all five elements today. Run the replacement for fourteen days, marking each day with a simple pass/fail. If you fail more than three times in the first week, the replacement is not delivering the same reward — redesign it before continuing.