Why Did You Doubt?

Matthew 14:25-31

25  And in the fourth watch of the night Jesus went unto them, walking on the sea.
26  And when the disciples saw him walking on the sea, they were troubled, saying, It is a spirit; and they cried out for fear.
27  But immediately Jesus spoke unto them, saying, Be of good cheer; it is I; be not afraid.
28  And Peter answered him and said, Lord, if it be thou, bid me come unto thee on the water.
29  And he said, Come. And when Peter was come down out of the ship, he walked on the water, to go to Jesus.
30  But when he saw that the wind was strong, he was afraid; and beginning to sink, he cried, saying, Lord, save me.
31  And immediately Jesus stretched forth his hand, and caught him, and said unto him, O thou of little faith, why did you doubt?