I think one of the best aspects of agile development is the ability for a team to frequently learn from their mistakes. It's especially crucial that this happens in a blame free environment. When something goes wrong during an iteration, it's important that no team member is singled out. The entire team accepts responsibility for their failures and successes together. And when a team makes mistakes, they need to learn from them. The key components for in a team's ability to learn from their mistakes are the attitude and interactions of the ScrumMaster.