Learn from experience
PRINCE2 project teams should learn from previous projects. They should therefore take initiative to uncover previous lessons learned and take these into account during the life of the project.
Projects are unique, meaning that there is always something new. This creates an element of risk in each project. We can also say that each project has some unknowns, which must be investigated. Now you can see why PRINCE2 urges the project team to take the necessary initiative to learn from similar projects that may have been done in the same company and if not, then get advice from other external people (for example, bring in external consultants).
“Learn from experience” covers the full lifetime of the project, from Starting Up a Project, as the project progresses until the Project Closes. Any lesson learned during the project should be documented. Documented lessons should be passed on so they are available for future projects.
PRINCE2 also states that it is the responsibility of everyone involved with the project to seek lessons learned rather than waiting for someone else to provide them.