Thank you for your thoughts.
I think the hard part about this is to create consequences that are bad enough that your characters don't drop it, but light enough that you don't wonder why in the world they agreed to the bet/challenge in the first place.
I probably lean to heavily on the soft side. I've only ever made bets where the loser had to admit to being wrong. I'm still in the middle of a bet, in fact, one that started when I was 13 will end when I'm 30, if I don't lose before that. To lose, I have to do a specific thing; to win, all I have to do is wait and not do that thing.
I made that bet with my older sister. Me being right and my sister being wrong was a big deal when I was a teenager. Me being wrong and my sister being right, as well. But now I'm in my mid-twenties, so it doesn't really matter. So, if I were to try and make a story out of this (which I've tried before, even before knowing about Dramatica), I would have to change a few things about this. Maybe shorten the limit to end at 16 instead of 30, and have the victory condition be a bit more than just waiting it out.
The thing about this bet is that, whenever I mention it to people, I get a lot of interesting reactions, because that thing I would have to do to lose is "normal."
The reason I thought about this question in the first place is because of a story I thought up recently where three teenagers decide to try a certain, rather inhibiting thing for a week, which requires all three's permission to proceed. If one drops out, all the others have to as well.They do it, they have some trouble, the week is over. In this case, the only real consequence for dropping it would be disapproval... which could mean a lot for teenagers, but I don't know. I'll have to work on it.