We assume that the universe is real, that it exists quite independently of human thought about it. But when we come to dealing with this universe, to human manipulation and improvement of it, we are not able to come to grips directly with this reality. We can only take in the sensory impressions reaching us from this real environmental universe, and from these construct a mental model of the universe as we know it.
Each of us must necessarily construct her/his own unique model. No two of us can receive identical data or hold identical viewpoints. In practice it turns out that the more direct one’s sensory contact and the more self-reliantly one builds one’s model (i.e., with the least uncritical borrowing of others’ conclusions), the more useful the model becomes.
These separate models which we build can be brought to any desired degree of agreement by communication and improved perception. Actually, conflicting viewpoints do not persist except where aberrations inhibit the thinking process… 
- Jackins, Harvey. The Human Situation. Rational Island Publishers, 1973. 62-63. [↩]