Why is it called lessons learned? Are there some projects that can be closed-out and documented easier than others?
A lesson isn't a real lesson unless it corrects something and/or changes something for the better. Thus, you haven't learned a lesson if you keep making the same mistakes over and over again. A project is supposed to be a unique event that will not ever happen again. Therefore, you can plan 50 parties in one ...
The author of this excerpt explains that change is inevitable during the life cycle of a project, but that project managers shouldn't allow occurrences whether negative or positive to dictate and/or deter project scope, or the outcome of a project.
For more information about lessons learned, please read the entire excerpt and view the information provided on this website by Jerry Madden: http://askmagazine.nasa.gov/issues/14/practices/ask14_lessons_madden.html . It provides a list of 100 Lessons Learned for Project Managers.