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