The Product Owner is invested to conclude the value that the user story will deliver, enabling him or her to set the backlog as per the highest priority. When a user story is created, it carries some value (we have also learned about it in the INVEST model where V stands for Value). When the sprint is being planned, the team pulls up the highest priority item from the pile for commitment. If the team members are picking up tasks as per their comfort, the scrum master has to come in picture and coach the team. Even the product owner might pick up stories which are not adding value to the customers.
