The September issue of Wired magazine featured the work of psychologist Paul Slovic which reveals that we as humans will rush to help a single stranger in dire straits while ignoring the masses who are suffering the same plight.
In one study, Slovic showed a group a photo of a starving child in Mali named Rokia and asked the members of the group how much they would give to help feed her. He then showed another group a photo of two starving children (Rokia and Moussa) and asked them how much they would give. He found that those shown a group of children (two or more) were willing to give 15% LESS that those who were shown only one child.
In another study, he found that people asked to donate money to help a group of dying children gave 50% less than people who were asked to donate to help one child.
How does this apply to marketing books? Simple. If you want people to respond to your the causes in your book, tell stories. But focus the stories on one person. Don't generalize. We do not respond to generalizations the way we respond to the plight of one person.
If you want people to be worried about global warming, don't talk about global warming. Too big. Too hard to grasp. Too hard to figure out how to help. Tell the story of one lone polar bear cub who is losing its home as it melts around him. We will respond to that.
Don't exhort people to be good to their neighbors or, God forbid, to strangers. If you want them to act better, tell them the story of the Good Samaritan. Be specific.