When your mother asks if you've taken a cookie you answer her no. That's a lie because you know for a fact you had that cookie and you are aware that you are giving your mother the wrong answer. Yes, I think so. I know what you mean. Although, realizing there is no one truth is sometimes a bit confusing.
People believe what they wish to believe.
Even if they know somewhere inside them that a message isn't true, they can trick themselves into believing. It is their choice. If they like what they hear and wish to believe in it, they will tell themselves to believe it. The message sounds right to them and makes perfect sense. What you should do is to trust your intuition and choose among the messages and the information you hear or read.