The Agile retrospective can be thought of as a "lessons learned" meeting. The team reflects on how everything went and then decides what changes they want to make in the next iteration. The retrospective is team-driven, and team members should decide together how the meetings will be run and how decisions will be made about improvements.
An atmosphere of honesty and trust is needed in order for every member to feel comfortable sharing their thoughts. Norman Kerth's work at the turn of the millennium was highly important to the development of Agile retrospectives and retrospectives in general. Kerth's prime directive states, "Regardless of what we discover, we understand and truly believe that everyone did the best job they could, given what they knew at the time, their skills and abilities, the resources available, and the situation at hand.