This is not a reasonable conclusion...you don't descibe what you mean by being "naughty". What did you eat? Was it a total carbfest? Did you overeat? If so, THAT'S the problem.

There's a lot ground between 20 grams of carbs per day (induction-level strictness) and a complete carb-meltdown. What you learned from your five-day cheat is that what you ate during that period will cause you to gain. That doesn't mean that you can't eat 30, 40, 50, or 60 grams of non-sugary carbs and still maintain your weight. Part of the process of low-carbing successfully is to gradually increase your carbs (by adding veggies, low-glycemic fruit, and so on) so that you can learn what your limits are.

Your experience makes it clear that you can't be "naughty" for five days without gaining. So you can't hope to maintain if you make that a habit. But that doesn't mean you are restricted to 20 grams of carbs for life. As you work the plan and move toward maintenance, you will figure out how to eat to maintain equilibrium. But low-carbing has to become part of your lifestyle, not just a temporary diet. Five-day excursions into a higher-carb way of eating need to be few and far between.