A man was about the cross a river, when master Vibhishana came over, wrote a name on a leaf, tied it to the man’s back, and said:
“Don’t be afraid. Your faith will help you walk on the waters. But the minute you lose faith, you will drown.”
The man trusted Vibhishana, and began to walk on the waters, without any difficulty. At a certain point, he had an overwhelming desire to know what his master had written on the leaf tied to his back.
He took it and read what was written:
“Oh god Rama, help this man to cross the river.”
“Is that all?” thought the man. “And who is this god Rama, anyway?”
The moment this doubt became lodged in his mind, he was submerged and drowned in the strong current.
From the Gospel of Sri Ramakrishna
Conclusion in Sri Ramakrishna's words:
"He Who has FAITH has everything, he who lacks FAITH lacks everything, it is the FAITH in the name of the LORD that works wonders. FAITH IS LIFE, DOUBT IS DEATH"
Source: Do Not Question the Search