I find it interesting that our first instinct is to believe that what someone is telling you is the truth. We don't immediately expect that we are going to be lied to, particularly if what we're told is said with confidence and authority.
We are particularly attuned to believing what authorities or those we care about tell us. It makes sense, because as children we need to trust what our parents are telling us and we need to trust that our family and community have our best interests at heart. So I guess it can be hard for us to accept when we realise that someone we trust has been lying to us.
Then when it's something we want to hear or believe, it becomes even harder to deal with the fact your being lied to. Often we can end up telling ourselves lies to defend the liars, because we want to believe they've changed and that they won't continue doing what they're doing.
So reliant are we on others doing the right thing that we can be unsure of ourselves if others around us are doing differently. Have you ever pulled off at the traffic lights when they turn green, only to second guess and wonder if you've made a mistake because the cars next to you haven't moved? You might double check that the light is actually green or look for the flashing lights of an emergency vehicle, in case they saw something you didn't.
It's particularly hard not to doubt ourselves when the majority around us believe something different. If the masses believe something then anyone who believes otherwise is going to stand out and that's usually a dangerous thing. Yet throughout history it's been proven time and time again that the majority weren't always the right ones.
It’s interesting how the larger the scale, the more effective the lie is.
All this was inspired by the principle—which is quite true within itself—that in the big lie there is always a certain force of credibility; because the broad masses of a nation are always more easily corrupted in the deeper strata of their emotional nature than consciously or voluntarily; and thus in the primitive simplicity of their minds they more readily fall victims to the big lie than the small lie, since they themselves often tell small lies in little matters but would be ashamed to resort to large-scale falsehoods.
It would never come into their heads to fabricate colossal untruths, and they would not believe that others could have the impudence to distort the truth so infamously. Even though the facts which prove this to be so may be brought clearly to their minds, they will still doubt and waver and will continue to think that there may be some other explanation. For the grossly impudent lie always leaves traces behind it, even after it has been nailed down, a fact which is known to all expert liars in this world and to all who conspire together in the art of lying.
— Adolf Hitler, Mein Kampf.
People tell lies for a range of reasons. Often it's to protect themselves from what they feel will be judgement from others or to avoid getting into trouble when they know they've messed up. It's a form of manipulation which can escalate to the point of lying purely for personal gain, regardless of how it's harming others and it plays on that instinct of ours to believe.
When it comes from those you trust, it only ends up damaging the relationship and hurting those around being lied to. Do it often enough and you've lost their trust. When my daughters lied as children I'd tell them the story of The Boy Who Cried Wolf to illustrate why it was best not to lie. One lie can be forgiven as a mistake, but continual lying loses peoples trust and belief in you, then when you really need them, they won't be there.