Have you ever wondered this? I know I have, and as an ADHDer it is especially hard, because often times you lose focus and are on to creating the next greatest thing a habit. So you start a lot of great new approaches, but they never seem to stick.
Ann Graybiel of MIT’s McGovern Institute has shown through research that neurons change their firing patterns when habits are learned, and then change them again when unlearned. However, as soon as something kicks back in the habit, they are fired back up. That is why it is so easy to pick back up negative addictions like smoking and drinking, but also why if you establish good habits but lose them, you can kick them back up much easier as well.