The Talmud (Bava Batra 75a) records a breathtaking vision of the future Jerusalem: its gates would be made of single pearls, each pearl so enormous that it could be carved into a gate thirty cubits high and thirty cubits wide.
A skeptic once heard this teaching and scoffed. "You cannot even find a pearl the size of a dove's egg," he mocked. "Where would you find one large enough to carve into a gate?" He went away laughing at the absurdity of the rabbis' promises.
Some time later, the same man was sailing on the sea when a storm carried his ship far off course. In the depths of the ocean, he saw angels — or perhaps divine craftsmen — sitting and sawing enormous pearls into the dimensions described by the sages: thirty by thirty cubits. "Who are these for?" he asked. "For the gates of Jerusalem," they told him.
The man rushed back to the sage and said: "Master, teach! It is fitting for you to teach! I have seen exactly what you described." The sage looked at him coldly. "Fool. If you had not seen it with your own eyes, you would not have believed it? You mock the words of the sages?" And the sage looked at the man, and the man was reduced to a heap of bones.
The story's violence is deliberate. The sages were teaching that faith based on personal experience is no faith at all. The man who believes only what he can see is, in the deepest sense, already dead — because the entire structure of Torah rests on trusting what you have received from the chain of tradition, not what you happen to witness.