Just as planning encompasses all aspects of the sprint, the retrospective covers everything that is part of the sprint.
Often people tend to look at what went well or what went wrong during sprint execution. Why did we get stuck so long at getting that new tool up and running on Jimmy’s pc? How could it happen that we only discovered that team Jay had moved their user story, on which we depend, near the end of the sprint?
There is nothing wrong with questions like these. But we may be inclined to overlook that we may also want to evaluate what we may learn during refinement and planning. Even the way we hold our retrospectives may be part of the retrospective!