As much as people argue about the right way or wrong way to lose weight, or which foods to eat and which to avoid, or whether you're better off exercising in the morning or at night, or other differences of opinion ad nauseum, the one thing I think nearly everyone has experienced and cannot explain are those times when you do everything right and you gain, and the times you've been horribly bad but for some reason aren't punished at the scale. It happens. You just have to roll with it, and keep the "long view" approach foremost in your mind.