Hail mildly, pleasing solitude.
Companion of the wise and good,
But from whose holy, piercing eye,
The herds of fools and villains fly;
Oh! how I love with thee to walk,
And listen to thy whispered talk,
Which innocence and truth imparts,
And meets the most obdurate hearts. [ Thomson ]

Sure there is none but fears a future state;
And when the most obdurate swear they do not.
Their trembling hearts belie their boasting tongues. [ Dryden ]

Argument does not soften, but rather hardens, the obdurate heart. [ Dewey ]

There is no flesh in man's obdurate heart; he does not feel for man. [ Cowper ]

There is still a real magic in the action and reaction of minds on one another. The casual deliration of a few becomes, by this mysterious reverberation, the frenzy of many; men lose the use, not only of their understandings, but of their bodily senses; while the most obdurate unbelieving hearts melt like the rest in the furnace where all are cast as victims and as fuel. [ Carlyle ]