I wanted to clarify - Failure of the team in Sprints, otherwise called as 'learning' is ok. What about the failure in the role Scrum Master? For example, she is not able to build a culture of continuous improvement within the team?
A corollary is - When should the Scrum Master be fired?
Whenever the other Scrum Team members think best. They'd be advised to have clear evidence that the root problem lies with their Scrum Master, that the situation cannot be resolved by any better team action, and that another person is available who can do a better job.