Inde ferunt, totidem qui vivere debeat annos, corpore de patrio parvum phoenica renasci — Ovid, Metamorphoses
(A baby phoenix arises from the ashes of its father, destined to live for the same period of time)
My entry for the Snapecase, category three. The idea was that for the period of his early teaching at Hogwarts, at some point before he became settled there had to have been a long dark night of the soul. Voldemort's defeat and the death of Lily are destabilising enough, but being asked to teach and under what is essentially a type of house arrest can drive a person to very foolish things.