We're past the plagues, Egypt has been exited, and the Children of Israel are poised between the Sea of Reeds and the pathway to the Promised Land. Moses lifts his staff, the waters part, and the people march through as if on dry land. Pharaoh and his forces follow after, but the sea returns to what it was, and horse and rider are swallowed beneath the surface.
Three days later the Israelites are murmuring against Moses: "What shall we drink?" (Exodus 15:24). So God performs a miracle and provides potable water.
Less than three months out and they are murmuring again: "Would that we had died by the LORD’s hand in the land of Egypt when we sat by the fleshpots, when we ate our fill of bread, for you have brought us out to this wilderness to bring death by famine on all this assembly" (Exodus 16:3). God makes bread rain down from the heavens.
Again and again the Children of Israel will come to Moses with existential concerns over their continued nourishment - no matter how many times in the past God has come through and provided for them, each and every time there is a disruption the people go straight to despair.
The problem may be that the relationship between the nation and God is one of "what have you done for me lately?" as opposed to "what have you done for me always." The former takes a generation to generate the goodwill that undergirds the latter. The People have not been permanently impressed by the spectacle of the plagues; it is only after a generation in the Wilderness survived with the support of a loving God that faith - and trust - will come to be developed.