Refraining from assigning 'essence' to objects of awareness, especially the 'self'.
Like Anicca, Anatta is pointing to the inverse of a specific mental event, Atta. Atta is a little hard to translate, we can translate it as more like a verb or more like a noun (Pali is weird). If we see it more like a noun it might be translated as ‘essence’ and if we translate it like a verb it might be translated as ‘to take/have control/ownership of.’ Together we have the notion that if something has a real immutable character or ‘essence’ to it that we understand, then we can really control it and that this control won’t be subject to change. Anatta is to point out the error in this way of seeing things. The point is to notice the mental event that represents objects or concept as though they could or should be inherently or essentially controllable/ownable. If this were to just be taken on its own without the teaching of the antidote it might be called helplessness, that things are without the possibility of being controlled. We use the mind to falsely pretend we are more in control than we are. This faculty of mind feels like one of those child’s car seats that has a fake steering wheel on it, made famous by The Simpsons opening credits. The mind either deludes itself by carefully moving the fake steering wheel in line with what it sees so that it can pretend it has control, or it strains itself throwing its weight ineffectually into cranking hard on the wheel when the car goes places it doesn’t like.