A sign was given for the birth of a Messiah on the other side of the world. In the immediate world of the Nephites, after the day without a night, there were no more signs, no more miracles. As a phenomenon associated with nature, it was assumed to have some kind of natural explanation, and so many began to fall back into the routines of their daily lives. Their previous prosperity was returning, and with it their previous relationships with the culture surrounding that prosperity. With no better sign of a Savior than one that they could find a way to excuse, they returned even to a disbelief in the Savior whose sign they had seen.