Why did you Doubt?

"Come,¡± he said. Then Peter got down out of the boat, walked on the water and came toward Jesus. But when he saw the wind, he was afraid and, beginning to sink, cried out, ¡°Lord, save me!¡± Immediately Jesus reached out his hand and caught him. ¡°You of little faith,¡± he said, ¡°why did you doubt?¡± (Matthew 14:29-31 NIV)