Why must cell nuclei go through mitosis instead of dividing down the middle at random?

Inside a nucleus, the DNA is in a form called chromtin- it looks like a whole knotted up huge plate of spaghetti. If you just divded the cell down the middle, you'd end up with some important genes in one new cell, and other important genes in the other cell. Mitosis is a way of organizing all the DNA to make sure each new cell gets exactly the same thing: a complete set of DNA.