It is a paradox that Ed Miliband should sack Ed Balls, and that he could do so, yet he will not. Let us look at the three parts of this in turn. I say Balls should be moved to shadow foreign secretary not because I disagree with him. On the contrary, it is another paradox that Balls has been broadly right about the economy since the crash, although it is hard to be sure, not least because the difference between him and the Chancellor has not been as great as either of them pretends.
Balls would have kept public borrowing higher at the start of this parliament, which might have kept the economy ticking over at a slightly higher rpm than learner-driver Osborne managed when he nearly stalled the engine. As a result, tax revenues might have been a bit higher and borrowing might have been a bit lower now.
Balls should be moved not because of his economics but because of his politics. His performance in the Commons responding to last week's Autumn Statement was a disaster, albeit with a small "d". It should not matter that much. He made a simple, rectifiable mistake. He responded to the wall of noise generated by the Tory whips by shouting, just as they hoped he would. The more he shouted, the more they barracked, the redder he became, and the harder it became to listen to him.
A better actor – and any MP who wants to command the House, just as any teacher who wants to command the classroom, knows to be an actor – would have lowered his voice so that the Tories would have had to be quiet to hear him.
But Ed Balls has a larger problem, identified by his critics to left and right. Norman Tebbit, in the course of a grand-old-parliamentarian complaint about the "poor quality of the present generation of members", said the Tory tactics were misguided. "It would have made far more impact had the shadow Chancellor's response been heard in near total silence, save the odd snigger of disbelief."
Balls's big problem is the content of his speeches, not the delivery. Despite the heckling on Thursday, he stuck to a script, most of which he had written in advance. The problem was hinted at by Torsten Bell, Ed Miliband's economic adviser, in the email he sent to a colleague last month that went by mistake to a Tory MP of the same name. "As an example of why we're having problems on EB messaging – this is his current three-part argument: Cost of living; Recovery built to last; Economy works for working people. Nightmare."
Some people could not see what was wrong with Bell's account of Balls' "messaging", except, possibly, that Bell called it "messaging". I am guessing, but he could have been referring to Balls's style of "argument", which consists of arranging sound-bites in groups of three.
The sound-bites are not wrong. Who can argue with a recovery built to last? But they are hard to listen to. He does not sound like someone who has thought about his opponent's argument and who can explain why, however well-intentioned, it doesn't quite add up. That is an actor-teacher's skill, and he doesn't have it.
He has to persuade people that he can be trusted to run the economy. Meeting a wall of noise with a wall of slogans is not the answer. Being right about a technical question of demand management three years ago is not the answer either. People think the Labour government borrowed and spent too much. Which it did. It wasn't as bad as pretended by the Tories, who supported it at the time, and it wasn't the cause of the crash, but Gordon Brown kept borrowing at the peak of the boom. Balls, more than Miliband who was just as much part of it, is seen as sharing responsibility for it.
So Miliband should move Balls. He should not recall Alistair Darling. Darling disagreed with Brown, but not enough to resign and so he, too, shares responsibility for the past. Miliband should make Chuka Umunna or Stella Creasy shadow Chancellor. Someone with shock value and star quality, who was not an MP when Labour was in power. What is more, he could.
The Miliband-Balls relationship has been misread as Walter the Softy imprisoned by Balls the Bully. Actually, Labour would have benefited if Balls had been stronger, better able to resist some of the soft anti-market nonsense Miliband favours. For all that Tories like to portray Balls as a mafia-boss faction leader, it is hard to see how many divisions he could mobilise to stop Miliband moving him.
Indeed, one way in which Thursday's poor performance mattered was that it further weakened the Balls faction among Labour MPs, who want someone at the despatch box who makes them feel good.
Finally, then, to the third part of the paradox. I do not think Miliband will move Balls. Lulled by an average six-point opinion-poll lead, Miliband is oblivious to the urgency of Labour's credibility crisis. He thinks that he, Miliband, is winning the argument; that public opinion has shifted and is demanding a kinder, gentler capitalism. Perhaps he is right about that. I don't think he is, and I suspect Balls is sceptical too. But this is Miliband's election to lose and he must lose it in his own way.