The reason for using the Fibonacci sequence is to reflect the inherent uncertainty in estimating larger items.
Example:
| Fibonacci sequence | Estimated Time |
|---|---|
| 1 | shorter than half a day |
| 2 | half a day |
| 3 | one day |
| 5 | one and a half day |
| 8 | two days |
| 13 | longer than two days |