We improve our future performance by assessing a past performance. This includes identifying areas for improvement and creating an action plan for carrying out those improvements. If we implement our action plan, then our next performance should be better than the last. So while we can produce valuable information through assessing a past performance, without a future performance opportunity, any assessment is largely pointless.
There are some performances I think I would totally rock, if I were to assess my past performance and try them again: Extricating a mouse from a toaster is one that immediately springs to mind. But the chances of me ever repeating this performance are (thankfully) very small. So as much as I might be able to improve my ability to extricate a mouse from a toaster through assessing my past performance, carrying out that assessment in order to improve for the next performance makes no sense.*
It helps to divide our performances into two main categories: daily or frequent performances and seldom or one-of performances. Daily performances might include parenting tasks, learning, things we do as part of a career or job, and problem solving. Seldom performances could include things like giving a formal presentation to a large audience, interviewing for a new job, or learning a new language. What performance we sort into which category will obviously differ for everyone.
Frequent or daily performances are perfect for self-assessment because the next opportunity is guaranteed. For infrequent performances, the rarity of opportunity makes it hard to sustain intentional growth. If we want to improve and grow in areas where our performances are infrequent, then we need to generate opportunities for performing in these areas.
*Note that there is a difference between assessing a performance in order to improve the next performance and reflecting on or mining a past performance for information that can be used to generalize our understanding or solve a problem. Instead of spending my energy improving my ability to extricate a mouse from a toaster, some reflection on the instance helped me appreciate the utility of a toaster cover. And mousetraps.