Metaphors are at the heart of agile. From describing processes to providing a system vision, drawing comparisons with familiar reference points can provide the light-bulb moment that makes you understand a concept.
I am currently reading Scrum Mastery by Geoff Watts and the description Geoff gives of the servant-master role gave me the idea for a Scrum Master metaphor that I think describes the role well.
The metaphor is that of an usher:
“Ushers assist visitors by formally showing the way in a large building or to their appropriate seats. This may coincide with a security role.” – Wikipedia
This is a good description of a Scrum Master. The vast majority of the role is helping others: giving people directions, showing them to their seats, answering questions, helping to reduce distractions. A much smaller part of the role is helping people to adhere to the social culture, which means largely sticking to the rules that the majority of the people present support: keeping reasonably quiet, staying off the stage and remaining seated – whatever is appropriate in the given circumstances.
So a Scrum Master should behave like a Scrum Usher: enabling the team to do a good job and occasionally helping them to develop and adhere to their own team rules and culture.