Many teams and organization still believe that all items in the Sprint need to be finished in order to have a successful Sprint. After all, the team has given commitment, right? Not quite.
Because the word “commitment” is interpreted as “promise” by a lot of folks, there was a change in The Scrum Guide in 2010 stating that the Development Team doesn’t commit to completing the work planned during the Sprint Planning, but that they create a forecast of work it believes will be done and that this forecast will change as more becomes known throughout the Sprint.
The work to be performed in the Sprint is planned at the Sprint Planning. (…) The Development Team works to forecast the functionality that will be developed during the Sprint.The Scrum Guide™
Scrum is about reaching goals, not about finishing work items. There is value in goals, not necessarily in work items. A fixed Sprint Backlog is usually an indication of a missing Sprint Goal. When explaining a good Sprint Goal versus a fixed Sprint Backlog, I tend to sketch up the following image:
This image shows that a fixed Sprint Backlog takes away all flexibility to effectively reach the Sprint Goal and add maximum value in the Sprint. It kills all creativity and is a sign of little autonomy in the team. And overall it can be demotivating for team members.
The Sprint Goal gives the Development Team some flexibility regarding the functionality implemented within the Sprint. (…) As the Development Team works, it keeps the Sprint Goal in mind. In order to satisfy the Sprint Goal, it implements functionality and technology. If the work turns out to be different than the Development Team expected, they collaborate with the Product Owner to negotiate the scope of Sprint Backlog within the Sprint.The Scrum Guide™
In the Agile world it is common practice to develop in short iterations to make feedback loops as short as possible. The obvious iteration in Scrum is off course the Sprint with a length of 2 to 4 weeks, but there is a second, even shorter iteration; The Daily Scrum is actually a mini-planning where the Development Team inspects on a daily basis whether it is on track with regards to reaching the Sprint goal. It is a formal opportunity to adjust the plans and therefor adjust the Sprint Backlog if necessary.
If the Sprint Backlog would be fixed the Daily Scrum would become a status report meeting instead of a collaboration tool to inspect and adapt with the team. And it would become much harder to effectively reach the Sprint goal and add maximum value.
The Development Team modifies the Sprint Backlog throughout the Sprint, and the Sprint Backlog emerges during the Sprint. This emergence occurs as the Development Team works through the plan and learns more about the work needed to achieve the Sprint Goal.
As new work is required, the Development Team adds it to the Sprint Backlog. (…) When elements of the plan are deemed unnecessary, they are removed.The Scrum Guide™
We can conclude that the Sprint Backlog is indeed not fixed during the Sprint. It is a living plan to reach the Sprint goal and can change at any moment in the Sprint.