There is a line in James Graham's play This House, about the Tory and Labour whips offices from 1974 to 1979.
Graham puts it into the mouth of David Steel.
Maybe Steel actually said it - i don't know. Nor can I remember it exactly (I've only see the play twice - give me a chance!) But it suggested that Conservative governments collapse because they think they are destined to rule, and with Labour governments, it's the other way around - they collapse because they no longer feel they deserve it.
I keep on thinking about that over recent days when there are signs of the Conservative government unravelling - with two ex-prime ministers putting their heads back above the parapet. But really because they believe they have a divine right to run the nation.
That is how I understand the complaints from Jacob Rees-Mogg and Nadine Dorries about Sue Gray's agreeing to be chief of staff to a Labour prime minister.
It really is extraordinary that wwe have become so used to the idea that they are somehow members of our only natural party of government.
There are dangers inherent in all this, of course - and especially perhaps for Keir Starmer - that they might delude themselves that, in order to be elected, you had to be very careful to sound like competent Conservatives.
Or as former members of the SDP used to say in the eraly days of the Lib Dems - they have to be "serious about power".
It is also extraordinary how we have become martyred to the same divisions that have pulled the Tory party apart. it is horribly like the divided Conservative Party in 1905/6 - so cross with each other about 'imperial preference' that one senior minister described himself as "nailing his colours firmly to the fence" - that they let n the reforming Liberal government of Campbell-Bannerman, Asquith, Lloyd George and Churchill.
Yet somehow the decision by Rishi Sunak to replace the Northern Ireland protocol with a simple red and green lane was an unusual example of pragmatic common sense and compromise that has become sadly rare from British government recently. I imagine people thinking - why didn't we think of that?
But then, if an idea gets 'owned', it does tend to stop most governments from adopting it - so perhaps it was a good thing that its sprung ready made into the head of Sunak at the right moment. For some reason I can't imagine either Boris or Liz doing anything nearly as sensible.