"But when they saw him walking upon the sea, they supposed it had been a spirit, and cried out:
For they all saw him, and were troubled. And immediately he talked with them, and saith unto them, Be of good cheer: it is I; be not afraid.
And he went up unto them into the ship; and the wind ceased: and they were sore amazed in themselves beyond measure, and wondered.
What happened with the apostles in this case should not be surprising.
A fisherman can see a miracle performed with bread and easily accept it as miraculous: but perform a miracle on the sea, which he knows intimately, and he'll be shocked, amazed, and even afraid.
It was the bakers who were shaken to the core when Jesus fed the multitude with bread. Each of us harbors the greatest doubts in the area of his or her own expertise.