"Honesty is the best policy"
"Do unto others as you would have them do unto you"
Those seem to be words to live by.
THEN WHY DON'T WE???
To understand this, let's look at various types of lies:
1) White Lie: An often trivial, diplomatic, or well-intentioned untruth.
Stereotypical instances include moments such as when a wife asks her husband, "Honey, does this dress make me look fat?" or when that sketchy guys asks a girl out and she replies, "Sorry, I would love to, but I'm busy." We lie because we don't want to hurt others. We feel like if we sugar-coat things, we can protect them for the hard truth. But is that really the way to go? Our dishonesty can easily make situations go sour.
Example A: The husband tells his wife that she looks just fine. They go to her company dinner as she wears her way too tight dress; revealing things she would rather hide. Behind her back, the women from her work are gossiping about her clothing choice.
Example B: Having nothing to do on a Friday night, the girl decides she's going to get some ice cream at the grocery store to eat as she watches her favorite chick flick. At the store, she runs into that guy she turned down.
I'm not saying that losing tact is the answer--by all means--USE tact. However, also be honest. A "sorry I'm not interested" or "I like your green dress better" could have sufficed in these situations.
Patterns of white lies made over time can create distance between you and others, and destroy your credibility.
2) Black lie: the opposite of a white lie.
These are the most hurtful. They're lies created out of various forms of pride: selfishness, greed, haughtiness, etc. Sometimes we lie to protect or even enhance our image. As Cooley once said, "I am who I think you think I am". [Thank you Professor Child] I'm sorry, but the truth is that if you made a choice to do/be something, own up to it. If you're afraid of repercussions that will ensue from your poor choices, then don't make those decisions. Your current choices define who will become. Not that you can't change--but if it's really in your character to make a decision you're not proud of, then you shouldn't be so defensive about people finding out.
Granted, no one's perfect--which is a reason why we shouldn't judge others. We don't know where they're coming from. However, fear of judgement isn't a legitimate reason to lie.
