Peterson`s interest in writing the book stemmed from a personal hobby of answering questions posted on Quora; One of these questions was, „What are the most valuable things everyone should know?“, to which his answer included 42 rules.  The original vision and promotion of the book was to incorporate all the rules entitled „42“.   Peterson explained that it is „not just written for other people. This is a warning to me.  Dorothy Cummings McLean, who writes for the online magazine The Catholic World Report, called the book „the most thought-provoking self-help book I`ve read in years,“ with its rules reminiscent of Bernard Lonergan`s and its content that „serves as a bridge between Christians and non-Christians who are interested in the truths of human life and resist the lies of ideological totalitarianism.“  In a review for the same magazine, Bishop Robert Barron praised the archetypal reading of the story of Adam and Eve and the Garden of Eden with Jesus, which represented the „gardener,“ and the psychological exploration of Alexander Solzhenitsyn and the Gulag archipelago, but did not support his „Gnostic tendency to read biblical religion purely psychologically and philosophically and not at all historically“ or the idea that „God. [is] simply a principle or an abstraction.“ It is „valuable to the besieged young men in our society who need a mentor to tell them to stand up and behave like heroes,“ Barron wrote.  Adam A. J. DeVille took a very different view, calling 12 Rules of Life „unbearably banal, superficial and insidious,“ and saying, „The real danger in this book is its excuse for social Darwinism and bourgeois individualism, which is covered in a theological patina“ and that „in a just world, this book would never have been published.“  Joe Humphreys of the Irish Times argued that people should not be deterred from „reading what is a true power of a book: wise, provocative, humorous, and also incredibly contradictory (as all deep and truthful studies of human nature must be).“  Glenn Ellmers wrote in the Claremont Review of Books that Peterson „does not hesitate to tell readers that life means pain and suffering.
However, his skilful presentation makes it clear that duty is often liberating and that responsibility can be a gift.  The book promotes the idea that people should be born with an instinct of ethics and meaning and take responsibility for seeking meaning above their own interests (Rule 7, „Pursue what is meaningful, not what is expedient“). Such thinking is reflected both in contemporary stories such as Pinocchio, The Lion King and Harry Potter, as well as in ancient stories from the Bible.  „Standing with one`s shoulders back“ (rule 1) means „taking on the terrible responsibility of life,“ bringing self-sacrifice, because the individual must rise above victimization and „live his life in a way that requires the rejection of immediate satisfaction, natural and perverse desires.“  Comparison with the neurological structures and behaviour of lobsters is used as a natural example of the formation of social hierarchies.    Ron Dart, in a review for The Ormsby Review, saw the book as „an attempt to articulate a more meaningful order for freedom as an antidote to the unpredictable. Chaos of our time“, but although „necessary“ with exemplary advice for men and women, it is „hardly a sufficient text for the more difficult questions that afflict us in our too human journey and that must be read as such“.   In a review for the Financial Times, Julian Baggini wrote: „In headline form, most of its rules are simply timeless common sense. The problem is that when Peterson fills them, they carry more stuffed animals than meat.  In the final chapter, Peterson describes the ways in which one can deal with the most tragic events, events that are often beyond his control. He describes his personal struggle when he discovered that his daughter Mikhaila was suffering from a rare bone disease.  The chapter is a meditation on how to keep a watchful eye on the small redemptive qualities of life (i.e., „petting a cat when you meet one“).