"Anyone can do the distance if they want it badly enough. There is no bigger challenge in triathlon than the Ironman distance, and ultimately the decision is yours and yours alone. The right answer lies inside you. You will do the training, you will make the necessary commitments, and you will miss out on certain other aspects of your life. For many, the trade is worth it. One is never "ready" for a ironman-distance race. The event is far too big for that. However, we firmly believe that anyone (and we mean anyone) can complete the distance so long as they have one ingredient: will. The will to train and, most important of all, the will to finish."
-- Joe Friel and Gordon Byrn in Going Long