Four letters, simple, seeming. But deep in its intricacies. There is a deep, throbbing pain, making the world turn red and forehead wrinkled as it soaks into your bones and drains everything but itself from the world, crowding out friends, family, music, sometimes even life itself. There is a short, sharp, deep pain, shocking and surprising, followed or preceded by a fall and broken pieces of human body pushed past their endurance. There is a pain upon moving, sharp and crisp and sexual with a grin or perhaps a grimace as the pain is relished as proof that one still lives, still loves, still endures. There is a pain of dreams dead, or dreams deferred, of things said or things unsaid, things done or things undone. There is the pain of living your life and realizing, suddenly, that all you have been, all you have done, is futile, hopeless, useless, adding nothing to this world, and that you are too old and too set in your ways to change.
Four letters. Pain. In the taxonomy of pain there are many pains, both physical and otherwise, temporary or enduring. There is only one truth about pain, and that is: there shall be pain. Perhaps not harsh, perhaps only wistful, but no life comes to its close in complete joy. Always there are the sorrows, the regrets, the could-have-beens and should-have-beens, the scars and the bruises and the scabs that are picked, and then comes the end with the needles and the cold. In the end all learn the truths of the taxonomy of pain.
-- Badtux the Somber Penguin