You Can't Verify What Your Son Is Saying

If you were the parents in that example, and this guy comes and tells you this, you probably want to hear some confirmations that what he's saying is true. You might ask questions that only someone who knew your son would know the answer to. But even having a very high probability opinion is not the same as believing. Believing involves an unconditional assent to the word of another. And when you make this act of trusting the witness, you are now knowing the truth that he knows but also have this relationship of trust.