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The team then holds a sprint planning meeting, where the team commits to delivering a set of cards within the sprint period. The team takes this commitment very seriously, and as result, much of the sprint planning meeting is dedicated to figuring out what deliverables are achievable within this short window of time. Before the team can commit to delivering a card, they must fully understand the requirements and estimate the size and complexity. After a few sprints the team's average velocity will emerge and the team will become more reliable at meeting commitments. Changing team composition during this time or after will result in less predictable velocity and likely missed commitments
It is important to note that team consistency greatly contributes to establishing a predictable velocity. When a new scrum team is formed, initial sprints will typically result in lower velocity than is the full potential for the team. As more sprints are completed with the same team, sprint team's dynamics, strengths, and weakness become more evident resulting in story assignments that are better suited for specific team members. When a team makeup changes across sprints, the new team member(s) introduces an "unknown" factor that will require few sprints for the team predictability to stabilize. Therefore, it is strongly recommended to maintain team consistency as much as possible to get the best results.
Committing to deliver a set of cards within a sprint is a team decision: the Product Owner and other non-team members assist by providing information and clarification only. As such, the team collaboratively estimates each card and jointly decides whether it will "fit" within the sprint. Many teams use an agile consensus-based estimation technique called Planning Poker to make these decisions, which facilitates discussion and encourages all voices to be heard.
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