What does it mean that capacity buffers?

Reserve some capacity for unexpected demands — running at 100% leaves no room for surprises.

Example: You schedule every hour of your workweek. Monday through Friday, 8am to 6pm, every slot filled: client calls, deep work blocks, admin tasks, team meetings. On Tuesday afternoon a major client calls with an urgent request — their product launch moved up two weeks and they need your revised strategy by Thursday. You look at your calendar and there is literally no space. To accommodate the emergency you cancel Wednesday's deep work block, push Thursday's admin tasks to the weekend, and skip your Friday one-on-one with a direct report. By Friday you have delivered the strategy but at the cost of three other commitments, each generating its own cascade of rescheduling, apologies, and half-finished work. One surprise did not just cost you Tuesday afternoon — it destabilized your entire week, because every hour was already claimed.

Try this: Open your calendar for the coming week. Count the total hours currently scheduled with specific commitments (meetings, deep work blocks, appointments, calls). Divide that by your total available working hours. If the ratio exceeds 85%, identify the lowest-priority commitments and move them to a tentative or optional status until your scheduled-to-available ratio drops to between 70% and 85%. Block the freed hours as "Buffer — Do Not Schedule" and defend them for one full week. At the end of the week, note how many buffer hours were consumed by genuine unexpected demands versus how many remained available for recovery or opportunistic work.