I have a tendency to get hooked on certain things (tv shows, books, etc.) and keep on with them until I wear them out.
This sometimes means watching DVDs of a tv show until I've watched them straight through (even if it's one I've watched several times before). [Ex. I re-watched all of my DS9 DVDs in the week or two right before beginning my undergraduate degree.]
This sometimes means reading through one book series until I've reached the end (such as catching up on old trek).
This sometimes means drinking only water or only powerade or only gatorade until I get sick of it.
That's probably why I never bothered to try alcohol or illegal drugs. I obviously have an addictive personality. Though, I do have a tendency to switch patterns eventually. It just takes a while, and it usually involves reaching a natural end-point (like the end of a show on DVD or the latest book in a series, etc.).