And we are about to be shown another classic lesson about it in Britain over the next four months.
Politicians cannot be trusted to stick to the issue.
They cannot be trusted not to hijack whatever question is on the block for their own purpose, be it Andrew Little on the flag, Jenny Shipley on superannuation or Boris Johnson on Europe.
That has been the case with New Zealand's own flag referendum, voting on which starts next Thursday.
Bear in mind that two years ago, when Prime Minister John Key first announced there would be a flag referendum, the reaction of the Labour and Green Party leaders was to welcome it and to say that they too would also hold a referendum if they won the 2014 election.
Between then and now, the leaders of the left have persuaded their supporters to oppose the process, criticise the cost, condemn the timing, question the motives, mock the alternative, and to vote "no change'' in order to embarrass a political rival.
They went into the last election promising a referendum on the flag and then cheapened the exercise because they wanted to portray it as Mr Key's and not the people's.
If Labour and Greens leadership had stepped above the political point-scoring and given their blessing to truly free debate on the left, David Shearer would not be the only Labour MP willing to say he is voting for the alternative among the 21 who were willing to say at all, and Kennedy Graham would not be the only Green MP voting for the alternative of the nine who were willing to say.
Hijacking the issue and potential sabotage will almost certainly occur in Britain's decision over whether to leave the European Union, or stay, as Prime Minister David Cameron wants.
It is virtually inevitable the June 23 vote will become, for many, a referendum on Mr Cameron's leadership - which is why he has been forced to state that he would not resign in the event of an "Out'' vote, even though he probably would.
Labour says it will campaign to stay in Europe.
But they won't be able to help themselves.
They will inevitably make it about the Conservatives, not about Europe.
The bigger threat to Mr Cameron's leadership is from within.
Popular and populist Tory politician Boris Johnson is using the referendum to bolster his own chances of succeeding Mr Cameron.
In a close vote, he could be a game-changer.
Mr Johnson's announcement on Sunday that he would be joining the Outers apparently surprised some of his closest friends who had never realised that Mr Johnson - the son of an ex-member of the European Parliament, and a former Brussels resident - was such a Eurosceptic.
One person not surprised by Mr Johnson's position was Sonia Purnell, a former workmate at the Daily Telegraph when he worked in Brussels.
She has also written a biography recording Mr Johnson's "blond ambition'' and fierce rivalry with Mr Cameron back to their Eton schooldays.
In The Independent this week, she said "Johnson has always believed that Cameron's job in Downing Street was rightly his: that he is cleverer, more original, more popular, more entitled to occupy the pinnacle of power in this country'' and in relation to his conversion to the leave-Europe camp: "Anyone with residual doubts about Johnson's desire to expel Cameron from the premiership could hardly fail to have read the signals.''
That said, a referendum to change the New Zealand flag is not in the same league as Britain leaving the EU.
Changing the flag in New Zealand is not going to have an impact on immigration numbers, the justice system, eligibility for benefits, trade deals or force the resignation of the Prime Minister.
New Zealand First MP Ron Mark has vowed never to cross the threshold of a business flying the alternative flag but that doesn't quite equate to an impact.
New Zealand First has played a straight bat throughout the flag debate.
It never wanted a referendum, it did not take part in the parliamentary committee and does not support a change.
But New Zealand First does have experience of what it's like to have pure politics hijack a referendum.
The 1997 referendum on a compulsory retirement savings scheme was negotiated by leader Winston Peters in the 1996 coalition talks with both National and Labour.
But it was a particularly toxic, post-election environment, both within the National Party and across the aisles with Labour, which had been spurned by Mr Peters.
(Labour would have won the Treasury benches if it had agreed to give him a turn at prime minister but it refused.)
Labour bagged the savings scheme ("Poodle releases turkey'', said Michael Cullen) only to introduce something remarkably similar, KiwiSaver, during its second term in Government.
National MPs were given a free vote on the Peters super scheme.
Jenny Shipley, who was secretly plotting for leader Jim Bolger's job, led the anti-savings scheme camp.
It was a prime chance for her to parade her leadership qualities to her colleagues and to deliver Mr Peters the comeuppance they thought he richly deserved.
Her support base had not adjusted to the realities of MMP and resented the intrusion of New Zealand First into a Government full of "born-to-rule pricks'', as Mr Cullen once described it.
But in the toxic political environment, the referendum became as much a vote on NZ First MP Tuku Morgan's underpants and the Tight Five as it was a vote on a compulsory savings scheme.
Not surprisingly, it was roundly rejected and Mrs Shipley rolled Mr Bolger the following month.
The superannuation issue had had a tortured path before it was finally put to a referendum in 1997.
Mr Key's flag issue hadn't been a burning issue, more a slow burner.
In a speech on March 11, 2014, at Victoria University - six months out from the election - he announced it would be put to a referendum after the election.
At least one thing Mr Key can't be accused of is rushing the process.
He wanted it separated from the election.
Officials worked on various options for how it could work and rated each's level of neutrality.
The most neutral process was chosen.
A committee of citizens ran the process.
It was a clean process.
Some of their choices were ghastly.
None was fabulous.
Some were OK.
The public chose the final alternative.
If you like it, vote for it.
If you like the present flag better, vote for it.
Don't let anything else get in the way.
Trust yourself.
● Audrey Young is The New Zealand Herald's political editor.
