When working on complex problems in complex environments, it cannot be guaranteed that applying a specific process or tool will fix the problem. Although, process and tools are important it's more important that people collaborate and try to find different solutions together and not rely solely on a tool to fix the problem.

The people who will perform the work make the final estimates.

At the end of a Sprint, the new Increment must be 'Done', which means it must be in useable condition and meet the Scrum Team's definition of 'Done'. Scrum Team members must have a shared understanding of what it means for work to be complete, to ensure transparency. This is the Definition of Done for the Scrum Team and it is used to assess when work is complete on the product Increment.

The Product Owner is the sole person responsible for maximizing the value of the product through the ordering and management of the Product Backlog. This reduces complexity in communication and understanding who to go to when there are Question:s about the product. The Product Owner may delegate his/her responsibilities but still remains accountable for the outcome of those responsibilities.