I had been puzzling about why for most of the past 12 days, until last night, the PM and his advisers had been insisting - in tweets, short videos and statements - that he was still running the show, in spite of the evidence that he was seriously and worryingly under the weather.
The answer, which is conspicuous this morning, is that although Dominic Raab has been asked by the PM to deputise for him when chairing important committees, including Cabinet, he is not 'in charge', in the way that a PM appointed by HM the Queen (and a Tory leader elected by Tory MPs and party members) would always be.
It is not his fault, but he has no proper mandate.
This absence of a conventional leader of the nation is complicated and concerning for two reasons.
First, and to state the spectacularly obvious, we face the greatest peacetime crisis of our age.
Momentous life and death decisions need to be taken: how lives are saved, how our prosperity is protected – and that's proportionately harder in the absence of someone unambiguously in charge, which Johnson was and Raab can never be (for structural, constitutional reasons).
It's all very well for ministers to say they are being led by the science and the scientists. But science and scientists simply provide the information on which choices have to be made. The buck stops with the PM and his Cabinet.
Second, and this also should not be ignored, the absence of a prime minister – even for a short while – is especially troubling when Parliament is not sitting.
To have a prime minister uniquely incapacitated, but the Government not able to be held to account by a parliament where true sovereignty resides under the British system, will be troubling for many.
All of which carries a series of important consequences.
One, as a senior member of the government told me, is that ministers will have to break the habits of a lifetime and put aside their vanity and personal rivalries. They need to show a spirit of collective endeavour.
But with the best will in the world, even if Michael Gove is proved right in saying on the Today programme that 'decisions will be taken collectively and following appropriate advice', they can't, for a while at least, be taken expeditiously, given that the Downing Street and Cabinet Office machines that serve the prime minister have very little working relationship with Raab and are (anyway) seriously depleted by illness.
All of which is to say that running the country is going to be nerve-wrackingly difficult for Boris Johnson's government in his absence.
And apart from Gove's collective Cabinet endeavour, the Government will also have to demonstrate unprecedented levels of openness and transparency about how and why decisions are being made, both with the opposition parties and with all of us.
To get through this, the whole country has to pull together, especially at a time when our precious freedoms are so constrained.
And in the absence of a prime minister, we'll only maintain that united front if our understanding of what the Government is doing and why is considerably deeper and richer than normal.