The notion of customary divine indication is central to the proof from a miracle: when the confirming event appears, God may bring about certain knowledge of the messenger's truthfulness in its witnesses.
Some theologians analyze this connection as an inference, while others emphasize the necessary knowledge arising under the established divine custom. Both approaches consider the particular prophetic claim and the confirming setting.
It does not follow that every unusual occurrence must indiscriminately validate every claimant who associates himself with it.
Something may remain abstractly possible in reason while sufficiently strong evidence yields certainty that it did not occur in a particular case. Possibility in the abstract is different from justified knowledge in a concrete setting.
An objection to miracles is that a claimant might still be lying. The response considers the complete evidential setting in which the divine sign is given and certainty is produced in observers.
Thus belief does not rest upon astonishment alone. It rests on the confirming relation between the sign and the claimant together with the mode in which that relation becomes known.