Despite her power, Granny Weatherwax rarely uses magic in any immediately recognizable form. Instead, she prefers to use headology, a sort of folk-psychology which can be summed up as "if people think you're a witch, you might as well be one". For instance, Granny could, if she wished, curse people. However it is simpler for her to say she has cursed them, and let them assume that she is responsible for the next bit of bad luck that happens to befall them; given her reputation this tends to cause such people to flee the country entirely. Nanny Ogg has obliquely implied this avoidance of magic avoids Granny being tempted into becoming a very successful "bad" witch.
Headology bears some similarities to psychology in that it requires the user to hold a deep seated understanding of the workings of the human mind in order to be used successfully. However, headology tends to differ from psychology in that it usually involves approaching a problem from an entirely different angle.
It has been said that the difference between headology and psychiatry is that, were you to approach either with a belief that you were being chased by a monster, a psychiatrist will convince you that there are no monsters coming after you, whereas a headologist will hand you a bat and a chair to stand on. The Headology approach is also very similar to Susan Sto Helit's practical approach to children's problems; since the child already believes in Bogeymen, then you may as well go along with it and teach them that they can also very firmly believe in the fireplace poker, too.
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