Parkinson's Law
Work expands to fill the time allotted.
C. Northcote Parkinson, 1955. The job takes the time available, regardless of how much time the job actually requires. Give a team six months for a two-month task and they'll find ways to use the full six months. Give them a week and they'll often hit the deadline.
The corollary is the Law of Triviality (bikeshedding): groups spend disproportionate time on trivial, comprehensible items (the bike shed) versus the important, complex ones (the nuclear plant). Everyone has opinions about the shed colour. Few have opinions about reactor physics.
For operators, the practical version: be careful about generous deadlines. They get used. Tighter deadlines often produce better-quality work because they force focus.
Examples in the wild
Most strategic planning exercises run to the time available. A two-week sprint produces a coherent plan. A six-month process produces a 400-page document everyone has stopped reading.
Investment committees often spend an hour on a small marketing budget and ten minutes on a major capital allocation. The trivial item is comprehensible; the major one isn't, so it gets less debate.
Household chores expand to fill weekends if you let them. The same chores get done in two hours on a weekday with a tight schedule.
Parkinson's Law is one of the mental models we apply through real cases inside the Pareto MBA — a part-time program for professionals who want to think clearly about business.