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

1. Label each time block with exactly one task or task cluster.
2. Close all tabs, notifications, and inputs unrelated to the single task before the block starts.
3. 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.