No one employs an architect whose house falls down, or a plumber whose own pipes burst. So why would anyone hire a branding guru who ruins his personal brand?

This difficulty confronts Kevin Roberts, chairman of the advertising agency Saatchi & Saatchi and “head coach” of its parent group Publicis. Mr Roberts resigned on Wednesday after provoking Maurice Lévy, Publicis chief executive, with remarks about women in advertising, angering colleagues and giving clients an incentive to fire his agency.

Mr Roberts is discovering something not taught in his books on advertising and branding, including the newly published 64 Shots: Leadership in a Crazy World. Corporate names are resilient: when their images get damaged, a change of management or strategy will often revive their fortunes. But personal reputations are fragile: mess with them and it can be fatal.