The lamp must be replenish’d, but even then
It will not burn so long as I must watch:
My slumbers–if I slumber–are not sleep,
But a continuance of enduring thought,
Which then I can resist not: in my heart
There is a vigil, and these eyes but close
To look within; and yet I live, and bear
The aspect and the form of breathing men.
But grief should be the instructor of the wise;
Sorrow is knowledge: they who know the most
Must mourn the deepest o'er the fatal truth,
The Tree of Knowledge is not that of Life.
Lord Byron, “Manfred”