Confirmation bias is essentially a phenomenon where preconceptions are reinforced by any means necessary, while evidence or other indications to the contrary are ignored or even go unperceived by the "investigator." A good way of thinking about this phenomenon is by imagining a child who's been made aware that one of his favorite toys is at the bottom of a toy box. The child may ultimately find only a generic version of the toy, or perhaps the toy is missing some of its parts, but the child still accepts it as what he'd been looking for. Meanwhile, in his excitement, the child throws other toys of potential interest behind him, completely absorbed by the search for the desired toy, thereby producing a tunnel vision effect.
Confirmation bias results from emotional attachment to ideas, and is antithetical to standard scientific inquiry. We should always attempt to disprove or discredit any ideas that we entertain. Furthermore, should we fail to actually disprove or discredit our ideas, we should still refrain from believing in them, while implementing them in our lives in a manner that makes it appear as though we believe in them. Never quickly say, "No, that's not what I'm looking for" as you mindlessly hurl a piece of evidence behind you, only to forget mere seconds later that you'd ever encountered it.