Lawyers sometimes run afoul of the legal ethics rules because they don't see a situation the right way. For example, a lawyer might fail to turn over a discoverable smoking gun document, because the attorney mistakenly convinces herself that the law permits that non-disclosure.
Professor Jon Hanson gave a very effective presentation at the recent ABA Conference on how our senses can deceive us, leading us to make poor decisions of this sort. My favorite example of how our senses can fail us was the McGurk effect. To see how it works, watch the man in the video below, and write down the sounds that you hear him making. Then listen to him again with your eyes closed. You'll see how easily your senses (in this case, your sight) can lead you to perceive the world incorrectly.