A simple layman armed with Scripture is to be believed above a pope or a cardinal without it. Our human reasoning alone isn't enough to discern truth from error. The best protection against deception is to know God's revealed truth, the Bible.
Truth is the road map for negotiating the difficult challenges of life.
Without it we get lost and we develop emotional problems that tell us we're lost. We often settle for half-truths or no truth at all because they are usually easier. But truth is the only road to emotional health. There is no other path.