difficult to understand

References in classic literature ?
Darcy came so often to the Parsonage, it was more difficult to understand.
It is so different from the country, and there is a great deal that is difficult to understand.
And now - well, I find even your attitude a little difficult to understand.
It was not difficult to understand that he had gained the crown of his ambition and that the silver-mounted wand he brandished was in his eyes as honorable a distinction as the marshal's baton which Conde threw, or did not throw, into the enemy's line of battle at Fribourg.
It is difficult to understand how, possessed of these combined attractions, she should remain Miss Brass; but whether she had steeled her heart against mankind, or whether those who might have wooed and won her, were deterred by fears that, being learned in the law, she might have too near her fingers' ends those particular statutes which regulate what are familiarly termed actions for breach, certain it is that she was still in a state of celibacy, and still in daily occupation of her old stool opposite to that of her brother Sampson.
He must have seen Cathy and her cousin about the spot before he examined it, for while his jaws worked like those of a cow chewing its cud, and rendered his speech difficult to understand, he began:-
Blanche who was not only as deeply involved as the other two, but also expectant of becoming Madame General and an important legatee--would not lightly surrender the position, but would use her every resource of coquetry upon the old lady, in order to afford a contrast to the impetuous Polina, who was difficult to understand, and lacked the art of pleasing.
Yes, I will stop," said I, "and I wouldn't have begun if you hadn't found it so difficult to understand my trouble.
It was, of course, difficult to understand, yet it was very evident that they did.
From the foregoing considerations it cannot be doubted that the geological record, viewed as a whole, is extremely imperfect; but if we confine our attention to any one formation, it becomes more difficult to understand, why we do not therein find closely graduated varieties between the allied species which lived at its commencement and at its close.
On the other hand, it is difficult to understand how a chief can arise till there is property of some sort by which he might manifest his superiority and increase his power.
How Falk had managed to turn the girl's head was more difficult to understand.