As Shearer's demise shows, that final step can prove to be a step too far for some politicians. It is a job where the workload is punishing, the frustrations are many and the expectations to deliver are utterly unrelenting, be it from caucus colleagues, the party's membership, or the wider voting public.
The latter can be the most cruel of all. Once voters had almost unanimously decided Shearer was never going to cut it, that was that. There was never any chance of a Second Coming.
The ignominy that Shearer will carry to his grave is that he is only the third major party leader since the Second World War to quit the job or be dumped without fighting an election in that role. The other unfortunates were National's Jim McLay and Labour's Sir Geoffrey Palmer. It will be little solace to Shearer that Helen Clark was but a few caucus votes away from joining that less-than-exclusive club back in 1996. The best that can be said is that Shearer's 20 months in the job saw him outlast Palmer by seven months and McLay by four.
Whoever succeeds Shearer - be it his deputy Grant Robertson, David Cunliffe or even one of the two MPs with only a very outside chance, Andrew Little and Shane Jones - will almost certainly still be at Labour's helm when next year's election rolls around.
While there is a relatively short time - just 16 months - for the new leader to impress voters, the timing of Shearer's departure has its advantages.
The new leader will have a strong mandate for shaking up the way Labour has been doing things thanks to the party's new rules which give the wider party a major say in who holds that job.
The worry of some in Labour is that the three weeks that the election will take to complete will only reveal Labour's divisions in more graphic detail and that it would be better for the party for the leading contenders to strike a deal which makes the contest a formality rather than a messy distraction.
The rank-and-file membership, however, is demanding it has its say and will be annoyed at any such caucus jack-up. That is now seen as unlikely. But if it happens, the resulting disgruntlement could boil over at Labour's annual conference in early November.
The party organisation is therefore demanding a proper contest, while also taking steps to ensure the outcome is not decided by a block vote by the trade unions affiliated to the party who have a 20 per cent say in determining the new leader.
If the contenders can avoid things slipping into acrimony - there will be a code of conduct which includes sanctions being applied to those who misbehave - the relatively long period set aside for the election could be invaluable in keeping Labour in the limelight and helping its efforts to reconnect with voters.
Indeed, the leadership election, the conference and the following byelection in Christchurch East, which will be triggered by Lianne Dalziel's tilt at the city's mayoralty, offer an unprecedented series of platforms for the new leader to establish his credentials with the public.
There is also the risk these events could end up being a string of calamities which could all but destroy Labour's chances of winning the 2014 election.
In regard to the byelection, Shearer was already trying to paint Labour as the underdog on the basis that Labour only held on to the seat in 2011 because of a strong personal vote for Dalziel. He suggested the electorate's true loyalties were better measured by National having won the party vote largely as a result of Labour voters having vacated the electorate in the wake of the earthquakes that had a devastating impact on that part of the city.
That does not wash. The numbers on the electoral roll certainly fell on 2008 levels, But that also happened in other low socio-economic seats around the country. Likewise with turnout. The blunt truth is that National's overall popularity and Phil Goff's poor performance as leader saw National make unprecedented incursions into territory which Labour took for granted as being its alone.
Shearer's defensiveness on Labour's chances of holding Christchurch East spoke volumes about his lack of confidence as leader. Byelections are normally referendums on government performance which is why governments fail to win Opposition-held seats.
Whatever, Labour must hold Christchurch East. Otherwise the party will be written off for the 2014 general election. A byelection defeat will only accelerate voter drift to the Greens and New Zealand First.
On a wider front, Labour's new leader will face exactly the same problems as his predecessor.
The first is the almost complete absence of a mood for a change of Government. The second is National's seemingly impregnable poll ratings. The third is Key's continued popularity despite the mishaps which have bedevilled his Administration.
Then there is Key's pragmatism, ideological flexibility and instinctive empathy with the largely conservative psyche of the great bulk of New Zealand voters.
Shearer never had an answer to these election-winning attributes. Neither did Goff. Maybe the new leader will come up with one. If there was an easy answer, however, Labour would surely have found it by now.
That all suggests the job of Leader of the Opposition is not about to get any easier.
