Ed Miliband has said he is still "recovering" from his time as Labour leader, more than six years after standing down.
He told the BBC's Political Thinking podcast leading the party to defeat at the 2015 election had been "gut wrenching".
"Frankly, your confidence gets shattered by losing," he told host Nick Robinson.
And he said the party's defeat was "in many ways" a personal rejection of him.
"More people wanted David Cameron to be prime minister than me, and I've got to accept that," he added.
Mr Miliband, who led Labour between 2010 and 2015, has since April 2020 served as shadow business secretary under current leader Sir Keir Starmer.
He said his decision to return to the shadow cabinet had been "really hard," adding: "the last experience of the front line was quite traumatic."
Asked whether he had recovered from his time as leader or was still recovering, he replied: "definitely recovering".
He added that being Labour leader had been "all consuming, and then it wasn't there any more".
He told Nick Robinson early polling data on election night 2015 "looked quite good" but turned out to be wrong, which made the party's eventual defeat even harder to take.
"You think you're going to be having the conversation with Barack Obama the next day, and then you're grateful for a call about your PPI," he joked.
Reflecting on his time as leader, he said: "I've come to the view that I had a big analysis of the problems of the country," but that his solution for dealing with them "were not nearly as bold, and not equal to the moment".
He added that he had "never really regretted" being Labour leader, a role which he took after defeating his brother David at a leadership election.
Elsewhere in the interview, he said Labour would "of course" have to be a patriotic party to succeed at future elections.
He added that the party's stance on defence and national security "was an issue" at the 2019 general election.
He was a panel member of a report which cited the issue as a factor in Labour's defeat, which left the party with fewer MPs than at any point since 1935.
Brexit and foreign policy were other policy areas judged by the report to have harmed the popularity of then-leader Jeremy Corbyn before the campaign began.
Speaking later at an event to promote his new book, Mr Miliband said his biggest regret was "not the sandwich" - a reference to a much-mocked picture of him in 2014 eating a bacon sandwich - but "not speaking in primary colours about the changes I want to see".
"I have become bolder as I have become older," he told the Hay Literary Festival.
You can download the full podcast on Friday 4 June. It will also be broadcast on BBC Radio 4 at 17.30 BST on Saturday 5 June.