My downfall is Diet Pepsi Max. You can tell me how poisonous it is, how it stains your teeth, calculate the amount of money I've wasted on it, etc. So I'm doing the 30 day challenge. Then when my brain tries to bargain with me (you should do the official challenge, that doesn't start til the 12th) I can just tell myself "NOT UNTIL OCTOBER". There's just no bargaining with something that concrete (albeit arbitrary). I'm hoping the cravings will just go away and I'll get used to not drinking it.