It is really one of the great discoveries of the modern time; but, once admitted, it is a principle that does not merely affect politics, but philosophy, ethics, and finally poetry.
Browning was upon the whole the first poet to apply the principle to poetry.

He perceived that if we wish to tell the truth about a human drama, we must not tell it merely like a melodrama, in which the villain is villainous and the comic man is comic.

He saw that the truth had not been told until he had seen in the villain the pure and disinterested gentleman that most villains firmly believe themselves to be, or until he had taken the comic man as seriously as it is the custom of comic men to take themselves.

And in this Browning is beyond all question the founder of the most modern school of poetry.
Everything that was profound, everything, indeed, that was tolerable in the aesthetes of 1880, and the decadent of 1890, has its ultimate source in Browning's great conception that every one's point of view is interesting, even if it be a jaundiced or a blood-shot point of view.

He is at one with the decadents, in holding that it is emphatically profitable, that it is emphatically creditable, to know something of the grounds of the happiness of a thoroughly bad man.
Since his time we have indeed been somewhat over-satisfied with the moods of the burglar, and the pensive lyrics of the receiver of stolen goods.