The Power of Now is the title of a best-selling book by Eckhart Tolle: it has been read by millions. Another and earlier master of the art of life is Montaigne who urged his readers to withdraw to an inner room and respond to every moment. We should not dwell on our eventual demise but live fully and richly each instant of our lives. We must respond fully to each and every moment.
Be attentive.
Forced to live in the moment when in pain, especially physical, my instinctive response is to seek an escape, by whatever mental means, by not living in the moment. But I do understand what James is saying.