Clarity of vision.

In actuality, the best metaphor (in my opinion) is that of going to the optometrist. You go because you don't seem to be seeing clearly and you seem to be missing a lot of things and bumping into doorways and such more than you should. You have to go more times at first than you would the optometrist, but if all goes well you don't have to go back every year. If all goes well, your vision gets clearer and clearer as the years go by -- long after you stopped seeing the Doc. And -- you don't have to wear glasses or worry about contacts.