Sir Menzies Campbell has told the BBC he feels "irritated and frustrated" at having to resign as Lib Dem leader, but said the decision was his alone.
Sir Menzies, 66, said he could not get out from under the "cloying blanket" of questions about his age and leadership.
He said getting the party's policies across would be "continually difficult" with 18 months to go until an election.
He said he had "no sense" of people moving against him, but had stepped down in the interests of the party.
Sir Menzies' resignation on Monday evening came as a surprise to many of his colleagues. Earlier in the day, he had had to tell his wife Elspeth of his decision by telephone.
In an interview with the BBC's political editor, Nick Robinson, Sir Menzies was asked if he felt relieved at standing down, or frustrated at not achieving what he had set out to do.
He replied: "Irritated and frustrated. Irritated because of the quite extraordinary concentration of trivia which seem to surround leadership - people write articles on what kind of socks I wear.
"Frustrated at not getting the opportunity to lead the party in a general election, and I think our policies and our principles and our values would have been right at the very centre of the political agenda."
He said he had finally decided to step down after a week in which there had been "seven consecutive sets of reports about my age and about leadership".
He said he had to ask himself whether he would be able to sustain leadership until the next general election - which is not likely to be before 2009.
"Of my own personal qualities, I'm in absolutely no doubt, 18-hour days, my fitness and my stamina is as good as I would want it to be," he told the BBC.
"But I was by no means convinced, that we could get out from under this cloying blanket of speculation about leadership."
He said once he had decided on the "direction of travel", he saw no point in hesitating and had decided to step down "now", to give his successor time to "bed in", before the next general election.
He was asked if he would have had to go if senior colleagues had publicly backed him as the right man for the job.
Sir Menzies replied: "One or two colleagues said, shall we say, different things. But I did about six interviews at the party conference and in the course of that I was asked about leadership in every single one of these interviews."
Asked if anyone had said to his face 'Please go', he said: "No-one did, I promise you, that is absolutely the truth."
The race to replace Sir Menzies is already under way - early frontrunners to succeed him are Nick Clegg and Chris Huhne, but as many as seven are considering running.
Mr Clegg, the current home affairs spokesman, said he needed time to talk to his wife Miriam and "close friends" before deciding whether to stand for the leadership.
Mr Huhne has not said if he will stand - but sources close to him have told the BBC he is likely to make a statement on Wednesday.
Among others who have told the BBC they are sounding out colleagues about whether they should stand are Steve Webb, who is in charge of writing up the party's election manifesto, Ed Davey, Susan Kramer and Birmingham Yardley MP John Hemming.
Party president Simon Hughes, who has stood for the leadership twice before, has ruled himself out of this contest.
He told the BBC the party owed Sir Menzies "a huge debt of gratitude", and said he had taken "his own counsel", rather than being forced out.
But Lib Dem MP Mike Hancock is among those who believes Sir Menzies was hounded out by members of the party.
The party's chief executive and elections expert, Lord Rennard, denied he had been forced out, telling the BBC: "There wasn't a plot, Ming made the decision his own way yesterday."
Former Lib Dem leader Lord Ashdown said his advice to Sir Menzies would have been to go on his own terms.
The official contest to select a successor has already begun, with the winner due to be announced on 17 December.
Data not available for September 2006 and February and March 2007.