“Our sweetest songs are those that tell of saddest thought” explain from Shelley’s To a Skylark

We look before and after,
And pine for what is not:
Our sincerest laughter
With some pain is fraught;
Our sweetest songs are those that tell of saddest thought. (St. 18)
This is a stanza, taken from P.B.Shelley’s lyricTo a Skylark“, in which the poet speaks of the superiority of the bird’s song to man’s. While romantcising and idealising the skylark’s song, as an unparallelled joy, the poet here tries to explain why man cannot sing as happily as the bird.
In Shelley’s view, human songs lack the spontaneous joy which the bird’s song possesses, and consequently man fails to sing as rapturously as the bird. This is because man can never be truly happy. His joy of the present is shadowed by the memory, sad or sweet, of the past, and the fear of uncertainty about the future. Man seems to be haunted with a sense of restlessness and frustration and bears an inexplicable feeling of his failure to achieve and enjoy what he earnestly desires. Naturally, his laughter, even when this is thoroughly sincere, is not absolutely free, unmixed, but has a bitter tinge of sadness in it. Indeed, the quintessence of human life is found to lie in the profound sense of sadness and that is why all the great literary and artistic achievements of man-his great poems, plays, paintings, and songs are on the deep tragedy of human life. Sadness, and not joy, echoes best the inner urge of the human heart and prevents man from singing as spontaneously, as joyously, like the skylark, that has a clear vision of life and death.
This famous Shelleyan stanza is deeply philosophical and reflects on the grave truth of human life. The poet’s analysis of man’s failure to have the spontaneous joy of the skylark is quite commendable, although his explanation of the instinctive sense of sadness in human life may seem a bit exaggerated. But this is the exaggeration of a vital truth of man’s life.