Some people have trouble understanding fractions.
Now, let's say that I eat 3 of these pieces, and save the remaining 4 for later. That is what fractions are, numbers of pieces of a certain size. Instead of cutting the wiener into 7 pieces, we may decide to just make one cut, after we measure it with a ruler. Sometimes we want to leave it like that, as arithmetic may be simpler with the improper fraction. That idea is fairly simple.