Beware thou meddle not with timber trees but either at the change or full of the moon. Tiberius the Emperor observed likewise the change of the moon for cutting the hair both of head and beard. And yet M. Varro gave a rule, that to prevent baldness and the shedding of hair, the barber should be sent for always after the full moon.
~ Pliny the Elder, Natural History (Philemon Holland trans.)
My wife cuts my hair, but I’m always begging for a trim long before she’s ready to give me one. If I could marshal the authority of classical antiquity, perhaps I could fix her to a regular schedule. But whose prescription is more reliable? Tiberias Caesar, to judge by his statuary, was acceptably well-coiffed. The Oxford Classical Dictionary calls him an orator, a poet, and a connoisseur; but then it goes on to say that while ‘stories of vice on Capreae can be discounted, real defects, a cultivated sense of superiority, relentlessness and lack of affability, meditated ambiguity of language, remained.’ Marcus Varro’s habits of analysis, it says, were ‘sometimes carried to unhelpful lengths.’ Really, there’s nowhere to turn for good advice anymore.
The New Psalmanazar 