Just as we tend to assume that the world is as we see it, we naively suppose that people are as we imagine them to be. In this latter case, unfortunately, there is no scientific test that would prove the discrepancy between perception and reality. Although the possibility of gross deception is infinitely greater here than in our perception of the physical world, we still go on naively projecting our own psychology into our fellow human beings. In this way everyone creates for himself a series of more or less imaginary relationships based essentially on projection.
“General Aspects of Dream Psychology” (1916). In CW 8: The Structure and Dynamics of the Psyche. P.507