What is David Allen two minute rule?

Example: A developer captures a note during a meeting: 'Refactor auth middleware to use the new token format.' She looks at it during inbox processing. The actual change is three files and will take an hour. That gets deferred to her task list. The next item is a note that says 'Reply to Sasha — confirm Thursday demo time.' She could add it to her task list, tag it, set a due date, create a context label. Or she could pull up Slack, type 'Thursday works, 2pm?', and send it. Twelve seconds. The task is gone — not deferred, not tracked, not consuming a slot in working memory. She moves to the next item. By the end of her processing session, she has completed nine two-minute actions and deferred four substantial ones. Her task list is lean instead of bloated with trivia, and her mind is clear instead of tracking thirteen open loops.

This concept is part of Capture Systems in the How to Think curriculum.