Work on one task per block to prevent multi-task expansion
Assign each time block a single task — multitasking within a block causes both tasks to expand while neither gets full attention.
Why it works
Task-switching incurs a cognitive cost: returning to a task after an interruption takes time to re-establish context. When multiple tasks share a block, both suffer from switching overhead and neither gets the focused attention that accelerates completion. Single-task blocks eliminate the switching penalty and make the Parkinson’s Law constraint work as intended: one task, one clock, one stop condition.
How to do it
- Label each time block with exactly one task or task cluster.
- Close all tabs, notifications, and inputs unrelated to the single task before the block starts.
- If a new task arrives during the block, log it for later rather than switching to it.
Evidence
The cognitive cost of task-switching is well-established in cognitive psychology: switching time, error rates, and subjective effort all increase with multitasking. The application to within-block single tasking follows directly from this evidence. (observational)
Task-switching research is typically done on simple cognitive tasks in the lab; the magnitude of real-world knowledge-work switching costs is harder to measure precisely.
Sources
- Rubinstein, Meyer & Evans (2001), executive control of cognitive processes in task switching, Journal of Experimental Psychology: Human Perception and Performance
Common mistake
Keeping a second task "ready" in a background window during a single-task block — the availability of the second task is itself an attention cue that degrades focus on the first.
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More practices for Parkinson's Law, Made Practical
- Set deadlines shorter than you think you need
Assign a deadline that is tighter than comfortable — not unrealistic, but just tight enough to prevent scope creep.
- Time-box tasks instead of scheduling by list
Assign each task a fixed time block on the calendar rather than a position on an open-ended to-do list.
- Define "done" before you start
Specify the minimum criteria for a complete output before beginning, so you have a clear stop condition.
- Default to shorter meeting lengths
Schedule 25- and 50-minute meetings instead of 30 and 60 — the meeting expands only as far as the slot allows.
- Deliberately underschedule your day to prevent expansion cascade
Leave 20–30% of your workday unscheduled as buffer for tasks that expand beyond their box.
Related concepts
- Deep Work, Made Practical
Focus blocks, attention residue, and the shutdown ritual — with the evidence
- Time Blocking, Made Practical
Calendar blocks, day theming, and the deep/shallow split — with the mechanisms
- Essentialism, Made Practical
Less but better — the disciplined pursuit of less, trade-offs, and the mechanisms
- The Pomodoro Technique, Made Practical
The 25/5 cycle, the real mechanisms, and an honest read on the evidence