Ed Miliband left his extensive notes for last week's TV debates behind in the dressing room afterwards - for The Sun On Sunday to get hold of them and reveal how he wanted to come across to voters.
He hoped to come across as a "happy warrior", a phrase originally from a Wordsworth poem but often used by US politicians including Barack Obama.
It was among the motivational messages and prepared answers published by the tabloid.
Other reminders for the Labour leader's only chance to take on David Cameron directly during the campaign included turning negative comments into positive messages, remaining "calm ... never agitated", to "relish the chance to show who I am" and talk to the camera to "use the people at home".
Among the notes were several ripostes that he deployed during the two-hour clash between seven party leaders, such as urging voters to "use their vote as a weapon to fight for the NHS, by kicking David Cameron out of Downing Street" when challenged over wanting to "weaponise" the health service.
The claims that he said he wanted to "weaponise" the NHS during the election campaign have dogged him for months.
The Sun On Sunday's daily sister paper claimed Miliband's performance on Thursday "lost" him the election in its splash the next day.
The Sun On Sunday claimed the notes were the reason Miliband's performance was "robotic," but people were unconvinced it was all that remarkable for a politician to prepare for a defining event of an election.
@LadyMyler Only to readers who have had to do an exam, job interview, difficult pub quiz, best man speech or prepare for anything ever.— Stephen Bush (@stephenkb) April 4, 2015
I know The Sun want to stop Labour at any costs, but "Ed Miliband preps for a debate" is scraping a barrel made entirely out of desperation— Owen Jones (@OwenJones84) April 5, 2015
The front page quote the Sun have from Miliband’s debate notes is pretty endearing actually pic.twitter.com/NP3xOFaHw4— Mark Ferguson (@Markfergusonuk) April 4, 2015
ed miliband's decision to prepare for the leaders debate is a disaster for ed miliband says dan hodges.— euan mccolm (@euanmccolm) April 4, 2015
In a section of the notes where Miliband appears to set down his differences with the PM are the words "decency, principle, values".
Tories were quick to take the chance to mock the Opposition leader, deputy chief whip Greg Hands quipping:
Am not at all surprised that The Sun has Miliband's debate notes from Thursday. It was obvious that Ed didn't have them. #JustNotUpToIt— Greg Hands (@GregHands) April 4, 2015
One prominent Labour activist, Mark Ferguson of the LabourList website, said it was "pretty unforgivable" for someone to have allowed the notes to be left behind - but insisted some of the contents could be seen as "endearing".
A Labour spokesman said: "These notes will come as no surprise to anybody who saw the debate.
"They explain why and how Ed took on David Cameron over the NHS and living standards. They also show how Ed set out a positive vision for the future with Labour's better plan, including on zero-hours contracts, lower tuition fees and rents."
Written in 1806 and inspired by the death of Nelson, Wordsworth's Character Of The Happy Warrior has been cited by politicians for decades - most recently by Obama to describe vice president Joe Biden after they were re-elected to the White House in 2012.
It was also used by Obama's campaign manager Jim Messina - who has been advising the Tories 2015.