If we look through a piece of glass, irregularities and impurities may distort and discolor the impression of what we see. If we regard something through a convex lens, it appears to be upside down. But if we place a concave lens in front of the convex lens, we correct the distortion in the convex lens and things no longer appear topsy-turvy. Each one of us regards the world through his own lens, his own glasses. The effect of those glasses is that, even though we may be looking at the same thing, not all of us actually see the same thing. The lenses are ground by each individual’s upbringing, disposition and other factors.