Do you remember the "new Gordon"? No? I'm not surprised; you'd have to cast your mind back to a painfully short period in 2007. When Brown took over from Tony Blair, everyone told him that he had to change.
So the Prime Minister tried to be more collegial, more empathetic, more open to other people's views. He even tried to smile, and we all know where that got him. In the end, the new-improved-Gordon era lasted, what, a fortnight? No, I'm being uncharitable. It must have been more like a month.
I'm reminded of this when I talk to Labour politicians about Ed Balls, Alan Johnson's replacement as shadow Chancellor. Just as they did before Brown became leader, they all say: "Well, he'll have to change."
Most of them go on to say that he knows he has to change. And I don't doubt it. Balls knows he failed to win the leadership because of his personality, not his ability. Whether he can soften up, stop plotting and get on with his colleagues, though, is another matter. For, as many a disappointed spouse will attest, people don't change. We hope they will, they promise they will, but on the whole, they don't. It's a pretty reliable rule of human nature.
So what is Ed Balls's problem?
It's mainly one of arrogance, born perhaps of insecurity. Like Gordon Brown, he believes he's intellectually superior to almost everyone around him. He believes he's tougher and more driven, and despises others for what he sees as their weakness. And that includes Ed Miliband. "He just has contempt for him really," says one former Cabinet colleague.
The disdain comes not just from Balls thinking himself cleverer and tougher than the Labour leader, but also – until just a few months ago – Miliband's senior.
Balls was bullied at school for his surname and his stammer. He must have decided early on to turn himself into an aggressor. At his worst, he shouts at people, threatens them, humiliates them in front of their colleagues and briefs against them behind their backs. Of course, he can be charming too when it suits. But only when it suits.
This isn't good news for Balls's colleagues in the Shadow Cabinet. His is one of the few jobs in opposition that really involves engaging with other shadow ministers. Any policy proposal that costs money will have to be signed off by him. Already they are preparing themselves. "There are a few of us who are not going to sit there and be bullied," one Shadow Cabinet member told me.
Some of them get on with Balls perfectly well. Others have distinct reservations. "He and I have found that the best way of getting on is just not to talk to one another," said one yesterday. "I don't think Ed and I have ever had a proper conversation." If this bodes ill for Balls's colleagues, though, what about his leader?
Well, it depends which lessons Balls has learned from 13 years of dysfunctional Labour government. As Douglas Alexander admitted on The Andrew Marr Show yesterday, "The division and the factionalism did the party a lot of damage." He should know; he believes he was at the wrong end of Balls' briefings, despite having been in the Brown cabal.
If Balls is sensible, he will learn the right lesson from Brown's failures: that his old boss was never temperamentally suited to being Prime Minister and that his reputation would now be far higher had he played to his strengths and remained at the Treasury. Given that Balls has similar personality flaws and – like Brown – is never likely to be popular with voters, he should instead devote himself to being a brilliant shadow Chancellor who works well with his colleagues and is utterly supportive of his leader.
Worryingly for Ed Miliband, though, Balls will probably draw the opposite conclusion from recent history. He is much more likely to decide that Brown's failing was not to have pushed Blair out earlier. Balls was pressing Brown to do so from 2001 onwards, and his fundamental misreading was to believe that the then Prime Minister was weak and could be toppled if only Brown shoved a little harder.
Both Brown and Balls find it hard to understand their faults, and to change, because of their underlying personalities.
If you are already arrogant and convinced that you are right, you are less likely to listen to other people's constructive criticism. If you are very driven and your method of getting your way is to steamroller others into submission, then it's hard to persuade yourself to ease off the accelerator. And if you hold obstinately to positions – as both Brown and Balls did over their refusal to countenance the language of cuts in 2009 – then it's much harder to back down and persuade people that you have changed.
The Tories, although they know that Balls will be a forensically aggressive opponent, are ready to capitalise on these flaws. They doubt that he will be able to bring himself to make the embarrassing climbdowns necessary to disassociate himself from Brown's failures. After all, he was City minister during the far-too-light regulation of the banks; his was the strongest voice, alongside Brown's, against reform of the public services; and just a few months ago, he was calling Alistair Darling's plan to halve the deficit in five years a "mistake".
If Tony Blair was the Teflon Prime Minister to whom nothing bad stuck, they expect Balls to be the Velcro shadow Chancellor. Every time he attacks the Government, George Osborne will be able to say, "I'll take no lessons from the man who failed to regulate the banks/opposed foundation hospitals/ saddled us with a huge structural deficit [delete as appropriate]."
Balls does, however, have an intellectual confidence and drive that will serve him well in opposition. After years spent in the Treasury, he will know where the embarrassing figures are buried in the Red Book. Beyond sticking to the Darling deficit plan, he will devise his own policies for the party.
"It's wholly implausible that economic policy will be determined by Ed Miliband," says one Labour frontbencher.
Balls will hope that the stronger he appears in opposition, the more he will succeed in overshadowing his leader. If the mutterings mount against Miliband, he will be in the best position to capitalise on the discontent (though he must learn to hide that smirk when talking about his rivals' troubles). What he does know, though, is that – unlike Brown – he will have to face Labour's selectorate again if he is to take over as leader.
Given that he has already been rejected once for character reasons, he can't risk being exposed for a plotter again. So Balls is going to have to act for now as if he respects his colleagues and his leader. He will have to force himself to be scrupulously polite and to forswear negative briefing.
Can Balls break all his old habits? I doubt it. But even if his transformation lasts for longer than Brown's, Miliband will never know for sure whether it is sincere. Until last week, the Labour leader was fighting just the Government. Now he is fighting on two fronts. That can only be bad, for him and his party.