PRINCE2 project teams learn from previous experience. Lessons are recorded and acted upon throughout the life of the project.
Projects commonly include a unique element or characteristic that means that it cannot be managed by existing line managers in an organisation. It is this uniqueness that makes managing projects challenging.
When starting a project: Previous or similiar projects should be reviewed to see if lessons learned could be applied. If it is the first of its kind for an organisation then it is more important to learn from others.
As the project progresses: The project should continue to learn. Lessons should be included in all reports and reviews in an attempt to seek opportunities to implement improvements during the life of the project.
As the project closes: The project should pass on lessons. Unless lessons provoke change, they are only lessons identified (not learned).
It is the responsibility of everyone involved to seek lessons learned rather than waiting for someone else to provide them.