I like Valerie's 90/10 explanation. I think this is what I do (with some exceptions. Like, I will never again willingly or comfortably eat bread). If we go out to eat, I'll have some corn tortilla chips. Or, if I'm dying for mozzarella cheese sticks, I'll have them. Just so long as the bulk of my meal comes from protein and fat, I'm comfortable eating a little crap -- but I don't do this every day. Once a week at most.
As for people who go off LC for more than a single meal -- I can't really wrap my head around how that works for them. I count on how I feel to tell me if I've eaten right. If I had two high-carb meals in a row, I think that internal barometer would start to go haywire, all my old cravings would rear their long-hidden heads, and (above all) I'd forget how I'm *supposed* to feel. Eek! The road to doom!!
It is a very personal issue, though. Maybe folks who can take the weekends off just have more discipline than I do, and therefore feel confident that they can force themselves back on the wagon even if their bodies are now telling them that there'd be nothing tastier than french fries.
PS I have a theory about this, actually. Some people have battled their whole lives with monstrous cravings for carby foods. I am one of them. Some people are overweight because they eat crap, indiscriminately and randomly, but they don't crave any particular foods. I think those people are the ones who have a better chance of eating off plan for a couple of days and then hopping right back on. It's people like me, who really can fall in
thrall to bread and sugar, that need to exercise more vigilance. (I also think it's people like me who benefit most from LC, and judging by the senior members of the board, they're also the ones who find the most satisfaction from eating LC. People who show up here who are just looking for a way to drop some pounds -- not a way to put an end to mind-wrecking cravings -- tend to find good success with things like WW as well.)