People who know a little bit of statistics - enough to use statistical techniques, not enough to understand why or how they work - often end up horribly misusing them.

How often do people harm themselves with statistics, rather than further their goals through deception? Scientists data-mining get publications; financiers get commissions; reporters get readers.

ETA: the people who are fooled are harming themselves with statistics. But I think the people want to understand for themselves generally only use statistics that they understand.