I think the point here is that most people have a large range of calorie consumption that they can maintain without gaining or losing much weight: there is a range of efficiency in the digestive process, your energy levels, unconscious behaviors like fidgeting, and variations on metabolic efficiency in general. These obviously won’t keep you from losing or gaining weight when the amounts are substantial enough, but that they can potentially overwhelm a few hundred calories in raw food consumption. Simple CICO calculations assume a constant food-to-useful-work ratio, but that’s an unrealistic model of the human metabolism. Hell, even my electric car does not have constant wall-to-wheels efficiency, it varies depending on voltage and battery state and whether the battery heater is active.