What does it mean that defaults can be designed?

You can deliberately choose what your default behaviors are.

Example: A software engineer noticed that her default response to finishing a task was to open Twitter. She audited the three drivers: environment (phone on desk, app on home screen), history (five years of post-task scrolling), and friction (one tap to open, thirty seconds to deep engagement). She redesigned all three — phone in a drawer during work hours, app deleted from home screen, and a sticky note on her monitor reading "next task or walk?" Two weeks later, her default after completing a task was checking her project board for the next item. She did not become more disciplined. She became better designed.

Try this: Choose one default you identified in L-1062. Write three columns on a page: Environment, History, and Friction. Under each column, write every factor that currently sustains the old default. Then, for each factor, write one specific change you could make this week to redirect that driver toward a new default. Implement all changes simultaneously and observe what happens for fourteen days, noting which drivers were most powerful and which redesigns held.