Can a first Sprint commence without a complete Product Backlog?

A first Sprint can indeed commence without a complete Product Backlog because Scrum emphasizes iterative development and the ability to respond to changing requirements. At the start of a project, it's common for the Product Backlog to be incomplete; it is expected to evolve over time as the team learns more about the product and gathers feedback from stakeholders.

A well-prepared Product Backlog does not need to be exhaustive before the first Sprint begins. Instead, it should contain enough items that provide value and allow the team to deliver a potentially shippable Increment. The focus is on the most important features that the team can work on first, which aligns with the principles of delivering value early and often.

This approach allows teams to gain insights through their work and engage stakeholders, leading to continuous refinement and prioritization of the backlog based on actual user feedback and changing market requirements throughout the development process.