My friend/mentor Gary likes to say that a good scrum master knows when to let a team feel some pain so that it can learn and grow, but he keeps the team from injury. It can be difficult at times to know if a team's decision will cause pain or injury, but it is a question that should be asked before rushing to solve problems for the team.
Scrum masters, agile coaches, and managers need to create safe environments for teams to experiment and grow. Yes, it can be nerve-wracking to watch a team make decisions contrary to what we would do, but learning may be stifled if the team is not free to make those "painful" decisions (again, we do not want teams to injure themselves). It is our responsibility to provide relevant information to the team regarding any constraints so it can make wise decisions, to encourage open communication and collaboration, and to eradicate fear through knowledge sharing.
One of the teams that I am coaching has its sprint retrospective this week, and there have been a number of challenges and issues that they've faced in the last 2 weeks that need to be discussed as a team; the scrum master and I chatted briefly about some of the issues that might come out during the retrospective and how to facilitate the meeting. As a facilitator, he needs to stay neutral in the content of the meeting so the team feels a sense of ownership in improving its processes, practices, and working agreements. He has decided to try the Constellation activity. It's a great activity to "hear" from all of the individuals on a team without pressuring people to talk, which can help quieter team members to feel safe. I've participated in this exercise a few times myself, and I am anxious to hear how the retrospective goes.