You start to satisfy the extra fat burn with calories after some time. It's easy to do, especially if you aren't being neurotic about food intake. So very slowly you begin sneaking in way more calories than you expect, because your food volume seems exactly the same.
That's where most of us get lost in an eating plan. We start to see the advances and then we want more. We supplement until we can no longer tell which supplement is doing what. This vexes our chances to be the epitome of all we wish to become, which is fitter.
We must at this point, become comfortable with discomfort...with what a mild deficit feels like, and understand that there is no change without struggle. Ask any fitness competitor or bodybuilder, how they feel on a regular day of restrictions, and how great they feel on their typical "cheat meal." It's the difference between staying on diet and completely blowing it. Here is a nice moment to consider that success lies somewhere between the extremes, though it still might be uncomfortable. I know. I've experienced it.