We all have scales on our eyes. The scales of the experiences we've accumulated over the years, the baggage we bring to any and every situation, the assumptions we make because of our own guarded, sometimes jaded, beliefs or opinions.
We can't help it, and yet it's absolutely necessary to understand how our eyes are clouded, and then set those notions aside at times. You've heard the phrase "check your assumptions at the door." It's a very important piece of advice, but first you have to know what your assumptions, experience, baggage are telling you. That requires keen self-awareness. Once you have that, it's much easier to check them at the door, or at least see them when they are coloring your thoughts.
I've noticed that the clouds over our eyes come particularly into play when we're dealing with other people. We make assumptions, and I bet those assumptions are wrong just as often as they are right. In the book, The Art of Possibility, Zander and Zander talk about "giving people an A." That is, assume first that everyone has the best of intentions, will perform perfectly, will live up to your expectations. Assume THIS, until PROVEN otherwise. This is a great way to check assumptions at the door, and likely be pleasantly surprised at least from time to time.