I laid their daggers ready;
He could not miss ’em. Had he not resembled
My father as he slept, I had done ‘t.

– William Shakespeare

Macbeth, Act 2, Scene 2. The cold and calculating Lady Macbeth shows a softer side of herself in this passage. She admits that the sleeping Duncan reminded her of her father, so she would have been unable to kill him herself. This shows that she is not entirely cold-blooded and foreshadows her later feelings of guilt.