But when he saw the strength of the wind, he was afraid and, beginning to sink, cried out, “Lord, save me!” Immediately Jesus reached out His hand and took hold of Peter. “You of little faith,” He said, “why did you doubt?”
Faith can feel strong right up until the moment it doesn't. If you're new to following Jesus, you may have had a stretch where trusting him felt surprisingly easy, and then one bad night of worry undid it. The fear came back louder than the faith, and you lost your footing.