Why shouldn't a story have all round characters or all flat characters?

If the story only has round characters, there will be too much information to take in, and it will be very long.

If the story only has flat characters, it will be boring, because nothing will change.

A good book/story should have both flat and round characters, because people would enjoy watching as the round character (usually the main character) changed, with flat characters surrounding them.

yea and yea x.x i love them =^-^=

the answer is both an appeal to ethos and logos (if that's what your question options were)