Once a teacher had a disciple who used to live in a hermitage. One day, the disciple was going somewhere. He hadn't gone too far when suddenly it started raining cats and dogs. He returned and told this problem to his teacher. The teacher said, "You should have faith in god. He will save you from all problems."
The disciple obeyed and resumed his journey. He kept reciting the name of god and cleared all the hurdles.
Next day, the teacher had to go on the same route. When he reached a deep drain, he doubted whether god would save him or not. The teacher got drowned.
Thus, doubt drowns you and faith saves you.