We have to learn to see the distortions brought about by the "lens" we use to see things: our own minds. This is quite difficult to achieve because when we look at our lens, we are using our lens to do the looking. So the lens can be unknowable.
Our ideas and beliefs--the things that shape our lenses--color our perceptions and analyses. But in order to become aware of the character of these factors we must somehow bypass them in our perception of our perception. It's quite a trick, actually. To turn the lens on itself is to step out of ourselves in a profound way.