I promise you that I am trustworthy. Heck, I hardly ever lie or distort the truth. So, go ahead and trust me.
Our natural inclination is to trust people. In "Social Intelligence" the author talks about mirror neurons that have been identified in human brains that trigger empathetic responses in us when we view something happening to another person. For example, when I was watching the Olympic 200m trials in Oregon last year I instinctively groaned and grabbed my hamstring when I saw Tyson pull up and fall to the track. I could almost feel the pain in my own leg and I got teary eyed watching the anguish on his face that was not only physical, but also the emotional atom bomb that he wouldn't be competing in the 200m race in Beijing where he was the favorite against Usain Bolt and Asafa Powell in both the 100m and 200m events.
We can usually trust people to treat us like they would expect to be treated because hurting you in effect hurts them too. But in some people, something goes awry and they simply don't have a clue on what is going on in other people. People with autistic spectrum disorders have this problem. They will consistently continue on and on talking about something long after it is clear to everyone that they are being a bore. If it seems like they don't have a clue, it's because they don't.
But another social behavior counter balances our trusting nature. When we discover taking advantage of our trust then we go into full out revenge mode. Traitors are reviled. The petty thief isn't trusted with the till. The convicted felon can't get jobs. The apostate is shunned by his former co-religionists or worse.
When you lose someone's trust, it's hard to get it back.
When I discovered that the Mormon church has systematically deceived me throughout my life I lost all trust in it and it's defenders and over time my distrust has been confirmed as I found more and more deceits and half truths. It turns out that the best source for unbiased information isn't always the source and in the case of the Mormons they only thing you can guarantee is that they'll only tell you the things that they think will be well-received. You see, they know what will turn you off so they give you "milk" before the "meat".
We can't function without some level of trust, but we need to develop a healthy skepticism so we can find who can and can't be trusted and once we find the untrustworthy change our default stance. Or as I constantly say in my line of work: Trust but verify.