That's what happened to me.

I used to play MMO frequently. While I would not play 12 hours straight, I played way more than what a healthy human being should devote his time into.

One day, one of my friend got unlimited (legitimate) GM access to one of the most popular MMO game in the world at that time, and I started 'padding' my characters with all sorts of extreme enhancements (+99, set items etc.) It was very fun to begin with.

After 3 days, my addiction was gone- It's like an epiphany- I suddenly jock awake and realized that, all the efforts you threw into the game will only amounts to a few bits in the game bits database.

I never got addicted to another MMO after that.

PS. But then, of course, the same concept also applies to the number on my bank account...but that's another story

(true story)