Why Is It So Hard To Stop Cracking Your Knuckles?

It is so hard to stop cracking your knuckles because it is not necessarily an addiction, but more of a habit. Many people subconciously crack their knuckles, so they don't even realize that they're doing it. It's extremely hard to get out of the habit of cracking your knuckles when you don't even realize when you're doing it. Another reason in which it becomes hard to crack is because your knuckles begin to feel as though they need to be cracked in order to feel good. (http://forums.xkcd.com/viewtopic.php?f=18&t=43826)