This idea, that the validity of a philosophy should be judged by the life of the philosopher, is out of fashion in current academic talk. In fact, as the author notes in regards to the final subject of the book, Friedrich Nietzsche:
"...it is one consequence of Nietzsche's own criticism of Christian morality that anyone who takes it seriously find it hard, if not impossible, to credit any one code of conduct as good for everyone, and therefore worth emulating."
Nevertheless, if a philosophy should not be judged by its philosopher, the life is not necessarily of no value. Hero worship is likewise considered old hat these days, but surely something can be salvaged in the example of those who came before us. Miller seems to think so:
"...each of these men prized the pursuit of wisdom. Each one struggled to live his life according to a deliberately chosen set of precepts and beliefs, discerned in part through a practice of self-examination...The life of each one can therefore teach us something about the quest for self-knowledge and its limits."
I have often thought of philosophy as a substitute for religion, and have found in the examples of mortal men greater hope than the deeds of gods or the promises of heaven. Life is a constant striving but, it is in what we strive for that makes the difference. If we seek truth, our reach may often exceed our grasp, but in the reaching we may just find our better selves.