Despite her power, Granny Weatherwax rarely uses magical power 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's cursed them, and let them assume she's 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.
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 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.