I don't know quite why you should say that
I don't know that I can do that
I don't know when I have heard anything so lamentable
I don't know why you should be displeased
I don't make myself clear, I see
I don't pretend to explain
I don't see anything particularly wonderful in it
I don't underrate his kindness
I don't want to disguise that from you
I don't want to exaggerate