A training metaphor I like:

Everyone thinks training is a linear path, "from here to there (eventually)" but it is more like a winding pathway around and up the mountain. As you follow the path, you continually end up right back where you started from: The same old scenery, doing the same thing over and over. It is sometimes easy to miss that even though we are in the same place again, we are just a few feet higher up the mountain. Sometimes the trail switches back and it seems as if we are now going backward but every turn brings us a few feet higher toward our goal. Thing is, when we finally reach the top (our goal) and look back, it seems so very far from the beginning. Then we look ahead at the next winding path and the next mountain, sigh and start climbing in circles again.