Calculate activity cost as disruption footprint: ramp-down + activity + ramp-up — the true cost includes attention residue

Why This Is a Rule

Sophie Leroy's attention residue research shows that when you switch from Task A to Task B, cognitive residue from Task A persists for 15-25 minutes, degrading performance on Task B. Applied to activity cost assessment: a 30-minute meeting doesn't cost 30 minutes — it costs 10 minutes of ramp-down (saving state, context-switching from previous work), 30 minutes of the meeting, and 15-25 minutes of ramp-up (clearing meeting residue, reloading previous work context). The true disruption footprint is 55-65 minutes — roughly double the activity's stated duration.

This transforms activity valuation. A "quick 15-minute check-in" has a disruption footprint of 40-50 minutes when ramp-down and ramp-up are included. Four such check-ins spread through a day consume 3+ hours of disruption footprint from "60 minutes of meetings." The activities were valued at their stated duration (60 minutes) when the actual cost was 3x that.

This is Multiply direct correction time by 3x for true cost — context-switching, opportunity cost, and verification overhead are invisible (3x cost multiplier for corrections) applied to activities: the stated duration systematically underestimates the true cost by ignoring transition overhead.

When This Fires

• When evaluating whether to accept a meeting, call, or interrupting activity
• When your day feels consumed despite having "few commitments" — disruption footprints are the hidden time sink
• When scheduling activities into a day and wanting to estimate realistic productivity impact
• When deciding between batching similar activities vs. distributing them throughout the day

Common Failure Mode

Valuing activities at stated duration: "I only have 2 hours of meetings today — that leaves 6 hours for deep work." With disruption footprints, 2 hours of scattered meetings consume 4-5 hours of effective time, leaving only 3-4 hours for deep work. The schedule felt open but wasn't, because disruption footprints were invisible.

The Protocol

(1) For any activity you're evaluating, calculate the full disruption footprint: Ramp-down (5-15 minutes): time to save state, mentally exit current work, and prepare for the activity. Activity (stated duration): the meeting, call, or interruption itself. Ramp-up (15-25 minutes): time to clear residue from the activity and reload context for the next task. (2) Total disruption footprint = ramp-down + activity + ramp-up. Typically 2-3x the stated duration for activities under 60 minutes. (3) Evaluate whether the activity justifies its full footprint, not just its stated duration. (4) Minimize footprint by batching similar activities (reduces transitions) or placing interruptive activities at natural transition points (before/after lunch, start/end of day) where ramp-up costs are absorbed by existing transitions.