Honesty is probably the most prized but least common quality in all of humanity. It's value stems from it's rarity but it doesn't make sense that such a seemingly simple and easy virtue is so lacking.
What makes it difficult is that there are different types of lying. Denotatively, it's just saying something that you know isn't true. But if that were all there was to it, things would be a lot easier. Bending the truth, leaving the truth out, pretending to be someone you're not, and cheating all supposedly constitute somebody as a liar. And if all of these actions are considered lying, then there is not a single person on earth who hasn't done it. We are all, in varying degrees, hypocrites. We share this sin but still have the audacity to feel hurt, offended, and heartbroken when we find out that somebody didn't tell us the truth.
I generalize because I see this so many times. "I can't believe you would lie to me!" "I can't believe you don't trust me!" "How can I believe anything you say?" People say this as if the only person that lies to them is the one who got caught. Even though we're diurnal creatures, we are constantly hiding and pretending. We perform for others and even when we're home alone, the make-up is still on. Everybody deceives, whether it be to strangers, our closest loved ones, or ourselves.
Even though it's considered to be such a grave and vile sin, the intentions behind lying are often good. We lie because we don't want to hurt anybody, especially ourselves. Sometimes people lie because they want to have "the best of both worlds" (excuse the Hannah Montana reference. There was no way around that one.) So we can have what we want without having to give anything up. Other times, we lie in order to protect people from knowledge that might hurt them. Most of the time, it's simply because there are things that have to be omitted; past experiences, dark secrets, parts of ourselves that nobody should see... Sometimes it's the simple and unavoidable fact that nobody is responsible for telling somebody everything about them. How public face and private face naturally differ and we want to impress people. All of these are selfish motives, but innocent nonetheless.
In the end, fear is what drives people to lie. And fear breeds mistrust, on both sides. When we lie to peers, we fear what they'll think of us. Whether they'll like the person we are less than the person we try to be. When we lie to parents or figures of authority, we fear punishment and even harm to ourselves. When we lie to family, it's because even the ones who have been there since day one still won't understand.
So, knowing how natural and unavoidable it is, why do people react so violently to be lied to? Personally, I think it's because when somebody lies to you, it shows brings out your own ineptitude. When somebody lies to you, it means that they don't trust you with that information, even though it should be you not trusting the one who lied to you. It also shows us how little we know about people. Our own ignorance is never more evident than when we depend on false information. We are fed what we want to hear and it tastes good and we're satisfied. But when we discover that the food we were given is something different, it's disgusting and we spit it out. That something different is reality and, like many of us are figuring out, reality is unpleasant.
I don't mean to justify lying and honesty truly is the best policy. But before we get consumed in how offended or betrayed we feel, we have to understand the person's motives. The root of deception is in fear, mistrust, and selfishness. If we want to be able to trust someone again, those three elements must be addressed and understood. Trust is a precious commodity and it's the duty of the trusted to earn it but also the duty of the one giving the trust to place it with a clear mind and understanding.