One common characteristic of pre-verbal toddler cognition is believed to be poor or absent object constancy: infants and toddlers may not understand that things exist objectively and permanently out of their sight. https://link.medium.com/px3zGYQ7U5 

When an object is in an infant / toddler’s field of vision, he can grasp its existence. When the object is removed, it may as well not exist. Out of sight, out of mind.

With time and the right experience, the child learns that objects, including his parents, come and go, but do not entirely disappear during the absences, and that he can depend on their existence.

This forms a basis of his sense of security, in the world and within himself, enabling healthy development of his cognitive and emotional capacities.

In cases of abuse, improper parenting, and/or trauma, the child’s development becomes disrupted or sometimes entirely arrested, leading to, among other possible outcomes, narcissism. One of its manifestations is believed to be an impaired object constancy capacity.

For an adult with the mindset characterized by the impaired object constancy, facts either do not exist objectively or do not matter, as they can be “disappeared” any time — gotten out of sight and/or wished away by closing one’s eyes, literally and figuratively.

Such an adult would have a very tenuous relationship with reality and the truth as most of us know it, and it is not because he’d be lying — in a sense of purposely bending the truth with a specific goal in mind — ...

...but because facts for him are not solid entities that exist outside of his field of vision (consciousness); rather they are things that enter and leave it randomly and/or at his wish.

We can see the poor object constancy reflected in a narcissist’s speech, which is infamously impressionistic: vague, light on facts and figures, and full of poorly articulated...

...but always self-centered feelings and self-referential emotion-laden observations which are based on his (mis)interpretations of reality, as his acknowledgment of facts is only cursory at best.

If object constancy is severely impaired, reality as most of us know it does not matter. Reality is not something existing objectively, outside of the narcissist’s mind, but is only his mind’s reflection, good and/or bad, depending on whether it meets or thwarts his need for...

...power and adulation. Unmoored from objective facts and not anchored in any values, such reality is always negotiable — to his benefit.

This is one reason why there is so often no discernible, coherent train of reasoning in Donny’s pronouncements, no logical connection between statement A and statement B, but rather seemingly disconnected emotional “jumps” based on either his deep-seated emotional problems...

(narcissistic insecurity) and/or fleeting impressions of any given situation / problem.

That sometimes his assessments do coincide with objective reality appears to be a matter of luck rather than a correct understanding of facts or any internal deliberations.