The Midrash writes that at mattan Torah Bnei Yisrael saw Malachim descending in precise order, in camps of degalim, and Bnei Yisrael desired the same for themselves. Moshe, however, complained to Hashem that to set up degalim would be an impossible task. No matter where he would tell a tribe to camp, they would argue why davka that spot and not somewhere else. If he would say camp in the east, they would inevitably (so Moshe thought) argue that they belonged in the west, and vica versa. Hashem replied not to worry, as the Shevatim already knew where to go. When Ya'akov's coffin was carried from Mitzrayim by the Shevatim, each Sheivet stood on a different side. They would accept the same pattern here.
Here we see a perfect example of the paradoxical nature of man so often stressed by the ba'alei mussar. Bnei Yisrael wanted to have degalim like angels, yet at the same time Moshe saw that they would bicker like children over whatever plan he would have to carry that out. We can reach for the greatest heights while at the same time being plagued by the basest desires and temptations. Why? Because as great as our intellectual achievement and ambition, at the end of the day we remain tied to our own base humanity. We unfortunately see this again and again in our day and age when people who contribute time and effort to building mosdos and doing great things are featured on the front pages of newspapers being led away in handcuffs.
So much for the hava amina of the Midrash. What are we to make of its conclusion? So what if years earlier the brothers arranged themselves in a certain pattern when they carried Ya'akov's bier -- why should the Shevatim in the desert accept the same arrangement? Ya'akov's funeral was an extraordinary circumstance, a one time event -- why would what was done then set precedent for what should be done generations later? I think the simplest answer is that precedent, even when adopted under extraordinary circumstances, is very hard to break. Once something is done even once, even is a unique circumstance, change becomes more difficult than simply accepting what was done.as the norm.
Any better answers? I've seen a few, but nothing that has grabbed me yet.