A team must be willing to commit to a goal, say an iteration goal. Commitment is one of the five core values of Scrum. Scrum provides people all the authority they need to meet their commitments. Some teams, specially newly formed teams, don't have iteration goals... not sure why; don't be like these teams. This setting of goal is easy, not a rocket science! Wire it into your team practice sooner rather than later. Once you have a clear and SMART goal, committing to its achievement is easy.