During the life of a Scrum project, the scrum team develops a shared understanding of how much effort a story point actually represents. This shared sense of worth of a story point makes estimates more accurate over time.

Story points are a useful measure of effort required for a task, even though they are not accurate. During the life of a project, the overestimates will cancel out the underestimates over many sprints. The Bell Curve provides a mathematics-based intuition for that assertion.