The people's patience was worn out by the journey

"From Mount Hor they set out by way of the Red Sea, to bypass the land of Edom, but the people’s patience was worn out by the journey;
so the people complained against God and Moses, “Why have you brought us up from Egypt to die in the wilderness, where there is no food or water? We are disgusted with this wretched food!" (Numbers 21: 4 - 5)

Scripture narratives are written to instruct us through the experiences of other people.  We learn what to imitate and what to avoid.  In Numbers 21: 4 - 5, we are reminded that the Christian life is a journey.  As the Israelites journeyed from Egypt to the Promised Land, so are we on a journey to the Promised Land of Heaven.  The journey could be long, tortuous and often on dangerous terrain.  There  is never an excuse for criticism, complaint or condemnation.  On the contrary, the word of God says:

"Have no anxiety at all, but in everything, by prayer and petition, with thanksgiving, make your requests known to god.  Then the peace of God that surpasses all understanding will guard your hearts and minds in Christ Jesus."  (Philippians 4: 6 - 7)

We shall never forget that:

"These things happened to them as an example, and they have been written down as a warning to us, upon whom the end of the ages has come." (1 Corinthians 10: 11)

"For whatever was written previously was written for our instruction, that by endurance and by the encouragement of the scriptures we might have hope." (Romans 15: 4)