I remember, in school, every so often our super-mean (but actually very good) math teacher would be away. The class would breathe a collective sigh of relieve as, rather than "Mr Mean" (names have been changed to protect the innocent), the replacement was usually an easy-going and amiable man who sat quietly, leaving us to get on without shouting or constant needling. He didn't insist on silence whilst we worked, he didn't much care how elegant our workings were on the page