In recent years, Jo Moore, Alastair Campbell and Damian McBride have all adhered to this unwritten law of political comms. It would seem that Andy Coulson - at the centre of the media storm over alleged phone hacking at the News of the World - is not so keen to play by the rules.
As I write, Coulson remains firmly in place as Downing Street director of comms. Despite seven days of negative headlines, many senior Conservatives are yet to be convinced of the need to jettison the Prime Minister's top media adviser.
Coulson has cling on so far largely because of the lack of any definitive evidence to prove he knew about illegal activities at the News of the World. But the Downing Street comms chief has also profited from the Labour Party's failure to cook up a coherent PR strategy.
With no leader and no clear direction from the top, the party has seen a number of actors wading in with a variety of different demands. In recent days, Alan Johnson has urged HM Inspector of Constabulary to investigate, John Prescott has talked of a judicial review, Tom Watson has demanded a full judicial inquiry and Keith Vaz has said that the home affairs select committee should investigate. If political hacks are mildly confused about what Labour wants to happen, it shows.
Nevertheless, the odds on Coulson leaving his job are shortening by the day. This week, the respected Independent columnist Steve Richards said he would be surprised if Coulson was still in post at the end of the year.
The wider problem for the Downing Street comms chief is that this is a story that first surfaced some time ago and is still refusing to go away. Despite valiant efforts to stay in the shadows, Coulson is now becoming a recognisable political figure in his own right, to the point where he is even the focus of newspaper cartoonist interest.
David Cameron will not be rash. He would be loathe to lose his highly regarded top comms man. But if Coulson fails to break free from the story soon, the PM may well decide that enough is enough. Alternatively, the frustrated former hack could easily make the move of his own volition. Neither outcome would surprise this writer.