Our assumptions form a lens that renders a convincing image in our mind. The lens can then begin to calibrate the relative value of evidence we see so that it reinforces the assumption. Because the lens produces certainty, but not necessarily accuracy, we may end up in a convincing cocoon of certainty even though it is potentially false. The problem with deception is, if we are deceived, by definition we are unaware of it. Many of us appear to confuse the certainty rendered through the lens built on our assumptions with the truth. The real tragedy is when we use that certainty to dismiss, disregard and even dehumanize each other… If we ride on the winds of our false certainty to diminish each other, we also become the the authors of our own poverty.
Here’s a more detailed look at confirmation bias: https://thewisdomoflife.wordpress.com/2012/06/09/confirmation-bias-what-is-it-why-is-it-important-and-what-can-we-do-about-it-2/