Flints may be melted - we see it daily - but an ungrateful heart cannot be; not by the strongest and noblest flame.
Robert SouthThat in all these worldly Things, that a Man pursues with the greatest Eagerness and Intention of Mind imaginable, he finds not half the Pleasure in the actual Possession of them, that he proposed to himself in the Expectation.
Robert SouthHe who does a kindness to an ungrateful person, sets his seal to a flint and sows his seed upon the sand; on the former he makes no impression, and from the latter finds no product.
Robert South