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Keep one root document per season
What the document holds
A seasonal plan, a quarterly plan, a semester plan, and a vision document are different names for roughly the same thing: a summary of what a person is up to over a stretch that usually runs two to four months. It lists the major goals, the habits and practices being followed, the metrics being tracked, and the systems used to stay organized. It gets pulled up during each weekly planning session, so everything else a person does traces back to it.
Length varies with the season. In one fall setup, the document is terse on purpose, because the semester is a sabbatical and the system starts out lightweight.
Linking bigger plans
Longer strategic plans for separate parts of life, such as a set of professional pursuits, live in their own documents. The root document pulls out what matters this season and points to them. Those big plans get read in detail when the root document is updated, and their core pieces are translated onto the shorter, time-limited plan. A simpler job may need no separate strategic plans at all, but some root document covering the current quarter, season, or semester has to sit at the center, with everything else described in it or linked from it.
Why do plans take longer than expected?
Psychologists Daniel Kahneman and Amos Tversky named the planning fallacy in 1979 to describe the habit of underestimating how long a task will take. In a 1994 study by Roger Buehler, Dale Griffin, and Michael Ross, psychology students predicted they would finish their senior thesis in 34 days on average. They actually took 55 days. Even their worst-case estimates averaged about 49 days.
Where did quarterly goal setting come from?
Andy Grove developed Objectives and Key Results at Intel in the 1970s, building on the management by objectives approach Peter Drucker described in 1954. Venture capitalist John Doerr learned the system at Intel and introduced it to Google in 1999. Google ran its goals in quarterly cycles, and Doerr's 2018 book Measure What Matters spread the method to many other companies.