I like metaphors. I can’t help but think that the roles of a Scrum Team could be compared to the three branches of government.
Executive Branch (Product Owner)
The role of the executive branch is to hold sole authority and responsibility for the daily administration of the state. They do not create the law, but are responsible for its execution.
In Scrum, the product owner is has the final authority to what gets delivered. They are ultimately responsible to the organization for the product. In some circles they are even considered the “single wring able neck”. The product owner does not perform the work but are responsible for it’s delivery.
Legislative Branch (Development Team)
The role of the legislative branch is to pass, amend and repeal laws. The legislature appoints it’s own leadership. They define who will do what duties and appoint their own committees. They congregate in the same room to deliver the work.
The development team’s role is to do the work. They appoint their own leaders and are self organizing in who will do what duties to complete the work at hand. They work in a team room to deliberate on the work.
Judicial Branch (SCRUM Master)
The role of the judicial branch is to interpret and apply laws on behalf of the state. They are critical in the resolution of disputes. They do not make laws and they do not not enforce laws, but rather interpret them and apply the facts.
In a similar way, the Scrum master interprets the principles/values of agile/scrum and applies them on behalf of the organization. They are critical in resolving conflicts and removing roadblocks to progress between the team (Legislative) and the product owner (Executive). They do not perform the work and they do not define the work or it’s priority, but rather they help provide balance and guidance for success.
When we start to think in these terms, perhaps it is easier to understand why one person shouldn’t hold two different roles at the same time? (ex: I’m the scrum master and a developer or I’m the scrum master and the product owner.)