How is a great poem created? It is a mystery. It is like asking for an explanation of a square cut by Gary Sobers or a cover drive by Rohan Kanhai. It is the same mystery that surrounds fundamental scientific discoveries.
One answer is that it is simply doing what it must. Shelley expressed this view:
“A man cannot say, I will compose poetry. The greatest poet, cannot say it; for the mind in creation is a fading coal, which some invisible influence like an inconstant wind, awakens to transitory brightness; this power arises from within, like the colour of a flower
which fades and changes as it is developed, and the conscious portions of our nature are unprophetic whether of its approach or its departure.”