As with all the most effective marketing tricks, granfalloon tactics prey on this fundamental human need. They manipulate you into feeling part of a group -- centered of course around their product, service, political party, or idea -- in order to obtain your allegiance and your money.
The social psychologist Henri Tajfel once conducted a simple experiment that demonstrates the power of granfalloon tactics: He brought a group of subjects into his lab and randomly, based only on a coin toss, assigned each subject to be labeled an X or a W. Each member of both groups was then asked to make a variety of assumptions about each of the other subjects. Though they were ALL total strangers, each person made MUCH more positive assumptions about those within their group than about those in the other group.
Social psychology is a fascinating area of study and Brian's article an interesting read.