The inherently creative nature of human beings means every exact description of what it means to be a human being is incomplete. As a result, any concept of the human that is attempting to be general must be vague. The human being can always develop, so it can develop out of the scope of any given description. So either we get a partial exact description or one that seems to be general but where the concepts involved have incomplete definitions (vagueness being a form of incompleteness, on the level of the definitions of the concepts used).
Fixing ourselves or others into roles that are strictly and formally defined, is thus dehumanizing.
We are partial, we are vague. That is what makes us human.