Confidence is not Truth

In dealings with people, confidence is everything. Anything said with confidence can be perceived as truth even though the two aren't related.

We've all got scammed at one point or another by someone who told us something that sounded like it was the truth because it was said with confidence. "I don't feel like he's lying" so we thought.
In a more extreme case, Hitler was using this approach to convince an entire Country that Jews were bad people and they should die. It makes no sense if we approach what he said from a logical point of view but it was repeated, with confidence, so often that people started believing in it.

Salesmen are thought to believe in what they are selling. To be sold on the product themselves if they ever wish to sell it to someone else. To believe in one's product is to have the ability to communicate its positives with such confidence that the listener will be sold on the idea as well.

What we have to do, as the listeners of those messages, is check the facts and form our own opinions.