Changing the leader can be one of the most difficult things a political party can do in a democracy, as the National Party is perhaps about to find out.
The process it may be about to embark upon could well be fraught with difficulties; it seems unlikely that it will find it as straightforward as Labour did last year.
The luck very much ran Labour's way in 2017. An accommodating, not to say selfless, leader in Andrew Little reached his own conclusion that it was time to go.
The Labour Party had already identified, in Jacinda Ardern, a deputy leader who could succeed to the leadership with a minimum of angst.
And, she was able to resolve one of the most difficult potential dilemmas faced by political parties – how to choose a leader who commands the support and loyalty of party activists while at the same time appealing to the wider electorate.
All too often, a potential leader who commends himself or herself to the party faithful will be a complete turn-off for the uncommitted public.
It was Labour's good fortune that their leader-in–waiting was not only the obvious and widely supported candidate from within the party, but that she immediately proved her vote-winning credentials with the wider public.
National, on the other hand, has a more difficult row to hoe.
Bill English is a widely respected leader, still enjoying support from his party and under no immediate pressure to go. While National has a deputy leader, there is no widely accepted successor but rather, as we are about to find out, a number of other challengers, each of whom will have counts against him or her.
None has quite the same freshness and novelty value that Jacinda Ardern displayed when she first emerged into the limelight.
National's contenders will all bring a certain amount of baggage with them into a leadership contest and, in an open democracy such as ours, any black marks from their past will be remembered and revived in the public memory.
Whether it was a disastrous television interview or pulling a fast one when a minister, the contenders will have to expunge those unfortunate memories and will have to hope that their supporters are a forgiving lot.
In modern politics, it will almost certainly be the case that a good deal of "qualitative polling" will be carried out in what are known as "focus groups" to find out just how the contenders are seen by the public.
I remember that, when I ran the 1987 general election campaign in the UK for the British Labour Party, we did this kind of polling, about both policies and personalities.
It came as quite a shock to us to discover that one of our leading spokespeople was a complete "no-no" for the public.
For party loyalists who are primarily looking for a leader who can win a general election, a demonstrated tendency to alienate undecided voters will ring the deal knell for a candidate's hopes.
Responding to a television interviewer rudely and aggressively, for example, may be seen by some as a plus, seeming to demonstrate leadership qualities, but not if it is a turn-off for the non-committed.
As the contenders line up, they will be hoping that they can start with a clean slate and will be forgiven past transgressions. Politics, however, is not usually so accommodating.
There is one further hurdle for them to surmount. Labour had to endure years of John Key's unusual ability to appeal to the voters.
The shoe is now well and truly on the other foot.
Now, National has the extra burden of choosing someone who can contest toe-to-toe with Jacinda Ardern. And that contest is not just about policies, important though they are – it is about the whole package, principle, personality, the lot.
Being as objective as I can, I cannot, when I survey the field of National hopefuls, see anyone who fills the bill from among the supposed frontrunners.
Favourites are usually favourites for a reason – but in this race, the favourites seem to have used the inside running to disqualify themselves.
Trying someone who is completely untried, on the other hand, is a huge risk, but it may be one that National feels compelled to take.