As forms of political communication go, the campaign theme song is among the lamest. It’ll be a special kind of nerd who treasures his copy of the Lib Dems’ mash-up of Uptown Funk, while the Green party’s boyband parody similarly prompted the toes to curl into a previously unknown and possibly dangerous position. And yet politicians’ choice of election anthem can be revealing.

For their part, the Conservatives aped 1992-vintage Bill Clinton by closing out David Cameron’s rallies with Fleetwood Mac’s Don’t Stop (Thinking About Tomorrow). Never mind that the song is four decades old, political types like it because it screams “the future”. And if there’s one thing candidates, their aides and highly paid consultants all agree on, it’s that a winning campaign must always own the future.

So established is this tenet of conventional wisdom, it’s spawned sub-tenets. Political operatives will tell you that “voters don’t do gratitude”, adamant that banging on about your past record is futile. Voters, they insist, decide based on “the forward offer”. What you’ve done matters less than what you’re going to do.

But what if this slab of received thinking rests on shaky foundations? What if, when it comes to politics, William Faulkner had it right – that the past is never dead, that it’s not even past? The thought is prompted by my Guardian colleague Patrick Wintour’s riveting account of Ed Miliband’s defeat, published this week. Over more than 6,000 highly detailed words, Wintour relayed the confessions of Labour’s inner circle on the missteps and blunders that took them to disaster on 7 May.

Just as it’s said that all happy families resemble one another – while each unhappy family is unhappy in its own way – so losing campaigns are always the most fascinating. In this regard at least, Labour did not disappoint. Wintour revealed those moments that only the sleep-deprived, neurotic intensity of an election campaign can produce, moments that hover on the cusp of comedy and tragedy.

So we learned of Miliband shutting himself in a hotel room, mortified by his failure to remember the bit about the deficit in his speech to last autumn’s Labour party conference. Or Harriet Harman, pushed out to face the TV cameras when the polls closed on election night, armed with a series of scripts tailored to every possible scenario – except for the one that actually happened. Or the notion of Labour’s finest brains sitting through 10 different meetings – 10! – each time approving the conspicuously absurd idea of the Edstone.

All of this is gripping for the reader, but make no mistake: even if every one of those missteps had been avoided, Labour would still have lost. Miliband is now on the backbenches, joking that he “used to be famous”, not because of temporary amnesia or a regrettable commission to a stonemason. Wintour’s report leaves no doubt that the central cause was Labour’s failure to have an account of its past – to answer the Tory claim that it was Labour overspending that caused the crash of 2008 and therefore ballooned the deficit.

Of course the rise of the Scottish Nationalists was critical, but chiefly because the idea of a Labour government dependent on the SNP fed into pre-existing fears, among English voters especially, that Labour’s leader was weak and that the party could not be trusted with the economy. The latter was all about the past.

I have sympathy for Labour people who urged Miliband to confront the Tory narrative: I experienced his rebuffing myself

No one can say this wasn’t predictable and indeed predicted. I have some sympathy for those Labour operatives now insisting they urged Miliband to confront the Tory/Lib Dem narrative of Labour fiscal incontinence, only to be rebuffed – because I experienced that rebuffing for myself.

In a conversation during the leadership campaign in the summer of 2010, I asked Miliband how he would counter the new coalition’s repeated claim that they were merely “cleaning up the mess left by Labour”. Surely Labour had to confront that claim soon, before it hardened into accepted fact. Hadn’t the 1978-9 “winter of discontent” branded Labour as unfit to govern, barring them from office for 18 years? I made the case as strongly as I could – restating it on these pages a few days before Miliband was unveiled as his party’s new leader – but he was unmoved. “I just think what we say about the future matters more,” he said.

Of course voters want to hear about the future, but only once they’ve decided that you’re worth listening to at all. If a vexed past means you can’t even get a hearing, then you have to deal with that past, no matter how painful. For Labour after 2010, that meant either devoting enormous energy to dismantling the coalition narrative – explaining that Labour spending was not always wise, but that it decidedly did not cause the crash or the deficit that followed – or surrendering to it, declaring Labour got it wrong. The first course seemed the wiser one to me, but either option would have been preferable to the path Miliband eventually took: neither confronting nor conceding the point, but simply hoping the voters would forget it and move on. It was that failure – not a mangled bacon sandwich or stumbling on a Question Time stage – that means Miliband bears great responsibility for Labour’s defeat, as he himself restated in the Commons this week.

It took 1992 for the nation to forgive 1978-9, and it took 2008 to wipe out the memory of 1992

Dealing with that past will now be a task for his successor. But the power of a poisonous legacy does not afflict Labour alone. The Tories lost their reputation for economic competence on Black Wednesday in 1992 and would have to suffer three election defeats before they were allowed anywhere near the steering wheel again. Sometimes only another economic calamity can erase the memory of the one before. It took 1992 for the nation to forgive 1978-9, and it took 2008 to wipe out the memory of 1992. On that timescale, Labour should brace itself for at least another decade in the cold.

This week reminded many who had forgotten that Charles Kennedy was the lone Liberal Democrat MP to vote against coalition with the Tories in 2010. He understood that voters’ memories are not as short as some politicians might like, that too many of them would remember the Lib Dems’ recent past as a party to the left of Labour, one that had denounced the Tories on everything from tuition fees to Europe. To change position so drastically, to break from their own very recent past, would be too much for most to stomach. The proof came on 7 May, when the electorate contemplated the gap between who the Lib Dems had become and who they used to be – and cast them out, Kennedy along with the rest of them.

The management gurus and political consultants may tell us always to face forward, never to look over our shoulder, to focus only on the future. But sometimes it cannot be done. In politics as in life, the past lingers.