After some recent discussion about the nature and purpose of these challenges, the moderating team have come up with some basic guidelines. Sobriety challenges should definitely have that goal as the focus - rather than more vague aims of controlled drinking - we have separate threads which deal with that.
However this shouldn't mean that mistakes are not tolerated, as occasional slips sometimes happen; but they can be opportunities to learn or reassess the situation - a valuable opportunity to discuss and get feedback from the other people on the challenge. And then if a 'one-off' mistake turns into several drinking episodes, it should be suggested to the person concerned that they try a 7 day challenge again, or even just a weekend.