A man’s abilities are seldom recognised by his family and others who know him well.
The source is Matthew, xiii, 57. Here is the story as told in the New English Bible:
When he had finished these parables Jesus left that place, and come to his own town, where he taught the people in their synagogue. In amazement they asked. ‘Where does he get this wisdom from, and this miraculous powers? Is he not the carpenter’s son? Is not his mother called Mary, his brothers James, Joseph, Simon and Judas? And are not all his sisters here with us? Where than has he got all this form?’ So they fell foul of him, and this led him to say, ‘A prophet will always be held in honour, except in his home town, and in his own family.’ And he did not work many miracles there; such was their want of faith.