Because it is occasionally possible, just for brief moments, to find the words that will unlock the doors of all those many mansions inside the head and express something—perhaps not much, just something—of the crush of information that presses in on us from the way a crow flies over and the way a man walks and the look of a street and from what we did one day a dozen years ago. Words that will express something of the deep complexity that makes us precisely the way we are, from the momentary effect of the barometer to the force that created men distinct from trees. Something of the inaudible music that moves us along in our bodies from moment to moment like water in a river. Something of the spirit of the snowflake in the water in the river. Something of the duplicity and the relativity and the merely fleeting quality of all this. Something of the almighty importance of it and something of the utter meaninglessness. And when words can manage something of this, and manage it in a moment of time, and in that same moment make out of it all the vital signature of a human being—not of an atom, or of a geometrical diagram, or of a heap of lenses—but a human being, we call it poetry.
from Poetry in the Making: A Handbook for Writing and Teaching by Ted Hughes