The Scrum Master must constantly explain both rules and rationale used to derive advice or correction. As an example, when a lower priority card completes and the team member asks for more work, the SM should not just advise, “Take the top item from the Product Backlog.”
But following discussion should occur: “Can you help expedite any card that is already in progress? If not, can you work on any of the committed cards that are not yet started? If not, is there a better way to redistribute work across the team based on your availability right now? If not, retrieve the highest priority item from the Product Backlog and commit only to as much as can be completed by the end of the Sprint.”