Figuring out "truth" is much like working a jigsaw puzzle without knowing what the end result is supposed to be. It's a challenging exercise from the start, but it's made far, far more difficult by our cognitive biases.
The only really effective way to work a jig saw puzzle when one doesn't know the end result is to let the the pieces already placed inform the attempted placement of each subsequent piece and then constantly update one's speculation about the end result with each successful or failed attempt. Becoming too rigid about what the end result might look like based on personal biases (as the religiously-minded usually do and as even scientists sometimes do) stalls progress. If the puzzle is actually a barn but you're absolutely convinced that it's supposed to be an airplane (because "God" told somebody thousands of years ago that it's an airplane), then you'll never work the puzzle. Ever. Rather, you'll actively resist placing pieces that make it look increasingly like a barn. And yet you'll never be able to arrange them in such a way that anything remotely like an airplane begins to take shape.
This type of intractable confirmation bias is the root cause of most human conflict--religious conflict, political conflict and even scientific conflict. Take as an example the debate between proponents of creationism and evolution. There are literally millions of puzzle pieces of evidence suggesting that speciation is a consequence of evolution by natural selection, and all these pieces generally fit together remarkably well (though not yet perfectly). Geology, ice cores, genetics, fossils, anatomy, etc. all suggest strongly that evolution by natural selection resulted in divergent species.
The puzzle isn't perfectly clear yet, there are definitely unanswered questions, and many puzzle pieces remain to be placed, but ever since Darwin first articulated his theory of evolution by natural selection, literally millions of once-scattered pieces have fallen neatly into focus. No other theory has proven capable of organizing so many pieces into a cohesive picture. And no evidence has been uncovered to date that conclusively contradicts the idea of speciation via natural selection.
Despite the fact that Creationism is no match for evolution when it comes to placing puzzle pieces, creationists resist. Even the most knowledgeable creationists (Michael Behe, for example) admit that their Creationism, or intelligent design, can't currently explain the evidence in the way that evolution can. Rather, they simply insist that an evolutionary understanding of the evidence is inaccurate and incomplete and that pieces that appear very well to go together actually don't (and that we'd understand that if we only knew what God knows). In other words, they insist that what appears very, very much to be a barn isn't a barn at all but is instead an airplane. This anti-barn and pro-airplane stance isn't anchored in observation (they readily admit that the developing picture LOOKS more like a barn than an airplane) but rather in simple confirmation bias.
A tell-tale sign that you may be suffering from confirmation bias is your ability to poke tiny holes in the argument of your opponent without being able to fully articulate a cogent alternative argument of your own. Creationism certainly meets these criteria.
