This is the lesson of the Harry Potter books, according to Peter Appelbaum, of Arcadia University in Pennsylvania, who has studied the morally ambiguous role played by Severus Snape, the potions master.
Professor Appelbaum contends that, while the series bears Harry's name, Snape is the real hero.
Initially, the books present a very dim view of pedagogy. Professor Appelbaum highlights the "unbearable and comic teachers" at Hogwarts. Snape, in contrast, is talented at spells, potions and mind-reading.
But it is not merely his subject knowledge that singles him out. While other teachers favour certain pupils, Snape acts as mentor both to Harry and to his arch-enemy, Draco Malfoy. He is the only adult who influences both equally.
As all teachers know, boys need male teachers to serve as role models. And while the books appear to hold up Albus Dumbledore, Hogwarts' eccentric head, as an ideal teacher, it is Snape who finally proves the better role model.
"Dumbledore is ultimately revealed as a victim of greed," says Professor Appelbaum. "Snape, in contrast, acts consistently on more noble motivations, sacrificing his life for the good of all humankind."
Tellingly, while there are no websites devoted to Dumbledore, Snape fan sites abound. "That's because Snape is sexy," says Professor Appelbaum.
But Snape's real strength is his ability to allow Harry to disobey him, so that he can learn from his own disobedience.
"Cultivation of self-will and self-sacrifice for a greater good demands that the apprentice dismiss the wisdom of the teacher," says Professor Appelbaum. "Trainers of teachers and educational policymakers may not want to think about this."