I think we all know of some one in our lives that has told us a lie. Once a lie, is told it is hard for us to believe in what that person says. I know a person that lies all the time, in fact when caught in a lie, this person will say they are sorry for lieing. No, they lie so much, they were just "sorry", they got caught!!
In fact they have lied so much, nothing they say can one believe. They may at one time have really be telling the truth, but since they have lied so much, one won't know when they are telling the truth. It doesn't even matter what it is, from the weather to health issues, they lie. So when they are actually telling you the truth you won't believe them because once when you did believe them, they lied.
It seems kind of funny that we can learn this lesson by an old children's story "The Boy Who Called Wolf." The little boy in the story would cry wolf while he was tending the sheep. Of course every one would run out to see what was wrong. The boy did this several times because he thought it was fun, getting attention. Until one day a wolf actually came and so when he yelled out "wolf" no one came!! No one believed him, because he had "cried wolf" before and nothing happened so people didn't believe him when some thing finally did happen.
I'm a trusting person and I like to believe what people say is true, but when some one has proven time after time that whatever they say isn't true, when something does happen I won't believe them.