…they had been driven out of Egypt and could not tarry, and provisions, too, they could not make for themselves. Not bringing provisions was irresponsible behavior and later it led the people to complain about food and water, so thought Rashi's grandson, the Rashbam. Rashi, on the other hand, explained it as a manifestation of the people's faith in God. Perhaps both are right: in the moment they truly believed that God would provide, but over time their trust in God declined. Faith is not static, it has its own ebb and flow, and even after we have it, we must work to keep it.