hard to understand

References in classic literature ?
But it is hard to understand why military writers, and following them others, consider this flank march to be the profound conception of some one man who saved Russia and destroyed Napoleon.
And if I said this, it would seem a poor thing and hard to understand.
My dear boy - forgive me if I find this a little hard to understand.
Lucille," he said, "I find you hard to understand to-day.
Mercy tried hard to understand him, and tried in vain.
I tried hard to understand the meaning of this question: but the persistent humming of the bees confused me, and there was a drowsiness in the air that made every thought stop and go to sleep before it had got well thought out: so all I could say was "That must depend on the weight of the potato.
You are my wife, but you would find it hard to understand them.
The reasons, operating in substantially the same way in all literature, are not hard to understand.
Razumov tried hard to understand the reason of this dumb show.
The problem is just as acute if we say that images differ from their prototypes as if we say that they resemble them; it is the very possibility of comparison that is hard to understand.
There was a very dark expression on his face; an expression that the Rogue found it hard to understand.
He blushed a good deal, and greeted the object of his late momentary aspiration to rivalry in the favor of a person other than the mistress of the invalid pug with an awkward nod and a rapid ejaculation--an ejaculation to which Newman, who often found it hard to understand the speech of English people, was able to attach no meaning.