Etcetra is right about the causes of many problems faced by students of all levels. I would include that once something is learned, it will never require any more practicing. Like the bike example, once you learn how to ride one you will always be able to ride one even if you haven't done so in years.If you find yourself continually practicing a piece you've "learned" then you haven't actually learned how to play it. If you find yourself having to "practice up" a piece, then you haven't actually learned how to play it.