This is the self-help book that is read by people who don't read self-help books. It contains none of the alluring promises of boundless joy and happiness that are the feature of personal development writing, yet has still been a massive bestseller. Famously beginning with the words, 'Life is difficult', it covers such gloomy topics as the myth of romantic love, evil, mental illness, and the author's psychological and spiritual crises.

Perhaps because of its lack of rosiness, it is easy to give this book our confidence. The Road Less Traveled is inspirational, but in an old-fashioned way, putting self-discipline at the top of list of values for a good life. If you believe there are no easy ways to enlightenment, and that things like commitment and responsibility are the seeds of fulfilment, then you are belong in Dr Peck's territory.

Peck is a conventionally trained psychotherapist, but has been influential in the movement to have psychology recognise the stages of spiritual growth. He sees the great feature of our times as being the reconciliation of the scientific and the spiritual world views. The Road Less Traveled is his attempt to further bridge the gap, and it has clearly been successful. The book is welcomed by anyone who has found themselves torn between the science of psychology and the spiritual search.

Our culture puts freedom on a pedestal, yet Peck recalls Eric Fromm's book Escape From Freedom, which looked at people's natural willingness to embrace political authoritarianism. It is referenced to support Peck's belief that, when it comes down to it, we shy from real freedom and responsibility.

The Road Less Traveled is rich with the stories of real people. Some of the vignettes demonstrate the transformation of a life, but in other cases people just refuse to change, or in the end can't be bothered. Ring true? It is in these less extreme cases that we are more likely to see our own quiet turning away from a bolder, richer life. Rather than the horror of a mental illness, Peck says, most of us have to deal with the straightforward anguish of missed opportunities.

Yet why is this so, when the rewards are so great? The road less traveled might be the spiritual path, but it is also a lot rockier and dimly lit next to the regular highway of life, which other people seem happy enough on. But Peck says that to ask this question of 'Why bother?', we must know nothing of joy. The rewards of spiritual life are enormous: peace of mind and a freedom from real worry that most people never imagine is possible. Burdens are always ready to be lifted, since they are no longer solely ours.

What is the fuel on the road less traveled? Love, of course, and Peck is at his best discussing this thing that cannot be adequately defined. We tend to think of love as effortless, the freefall of 'falling in love'. While it may be mysterious, love is also effortful; love is a decision: '...the desire to love is not itself love. Love is as love does.'

In his insistence on morality, discipline and admiration of long-suffering, Peck's writing can seem old-fashioned. Yet he is no conformist in his denouncement of the failure of psychotherapy to recognise people as spiritual beings, and the book has surprised many readers by its embrace of the Jungian, New Age concepts of the collective unconscious and synchronicity. Somehow, the blend of Christianity, the New Age and academic psychology works.