First Nephi 4:3

Now behold ye know that this is true; and ye also know that an angel hath spoken unto you; wherefore can ye doubt? Let us go up; the Lord is able to deliver us, even as our fathers, and to destroy Laban, even as the Egyptians.

Nephi could not comprehend his brothers' doubtfulness. To a believing heart, even the slightest hint of truth strengthens faith. To a doubting heart, even the strongest proofs are insufficient. We choose belief or doubt, and our choice colors all that we see and think. Nephi could not convince his brothers because they did not want to be convinced.