Is understanding a practice?

Enlightened people doesn't have any desire, because they see impermanence in everything. All the things are useless to them. To achieve enlightenment , one required to practise deattachment, uncertainty through out the samsara. So , Is understanding a practise ? 1. If it is: We loose skills when we don't do somethings for long time. But enlightenment can not be undone. 2. If it isn't: When we do vipassana meditation for a long time, we started to see impermanance in every day life. We loose attachments to lot of things . What is happening there ? I'm not sure I express and structured the question as I want . So Improves are well come.