It is necessary to the happiness of man that he be mentally faithful to himself. Infidelity does not consist in believing, or in disbelieving, it consists in professing to believe what he does not believe.
People are entirely too disbelieving of coincidence.
Several generations of high school students have grown up ignoring and disbelieving everything they've heard from government and police about drugs, including information that was factual and valid, because they discovered for themselves that most of what has been taught to them was simply not true.