Fibonacci Sequence

A mathematical sequence where each number is the sum of the two preceding ones: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89. In agile estimation, teams use a subset of this sequence (1, 2, 3, 5, 8, 13, 21) as card values for planning poker. The increasing gaps between numbers are intentional — they reflect the natural uncertainty in estimating larger bodies of work. It is harder to distinguish between a 20-day task and a 22-day task than between a 2-day and a 5-day task. The Fibonacci progression forces teams to acknowledge this imprecision and make deliberate relative comparisons rather than false-precision numeric estimates.