This an interesting book, recommended to me by Roland. Cooper first describes the teaching of Augustine as explained by Reinhold Niebuhr, in which pride is the quintessential sin. He then gives some feminist critique, especially because they see this view as too male oriented. Next he explains the view of Carl Rogers, who states that low self esteem rather than pride is the heart of our problem.
Cooper argues that both are present in everyone, though one may be more dominant than the other. But pride is often a mask for low self esteem, while people who appear to reject themselves, often do so because they feel they cannot live up to an ideal self that actually is impossible to live up to.
Both are the result of mistrusting God and rejecting Him as the source of our identity, self image and being.
Of course the book is much more elaborate than this very short synopsis. If you're interested in the question as to why people actually sin, this may very well be a book worth reading.