I begin this article with:

One of the most complex questions we can ask, “Why do we do the things we do?”, actually does have a very simple answer.  The answer is to avoid pain and/or to gain pleasure.

However, it is clear to me now that this is a gross over simplification of human behavior.  The article is worth keeping in the book, but it needs to be made clear that the avoidance of pain and the desire of pleasure is simply one of the many drivers of human behavior, and I would still argue one of the most powerful.