Sometimes all it takes to set off a landslide is the sudden dislodgement of a couple of pebbles.
Today, the "green" political brand is so potent that no major party can afford to issue a manifesto without at least paying lip service to its core principle of "sustainability".
It was not always so. Until the 1970s, New Zealand was still the sort of country where drowning lakes and rivers in the name of cheaper power was considered good politics by both the Right and the Left.
That was before the "Save Manapouri Campaign" - a mass political movement that for the first time successfully challenged, on a truly national basis, the view of "progress" that attributed no intrinsic value to New Zealand's wild and beautiful places.
That was the first pebble.
The second pebble was the Values Party.
Launched just a few months out from the 1972 general election by a young journalist named Tony Brunt, Values was the world's first "green" political movement to wage a nationwide electoral campaign.
Although Labour ran away with the 1972 election, the Values Party exerted an extraordinary influence on the campaign. Its superb advertising (produced virtually free of charge by a couple of sympathetic cinematographers at the National Film Unit) gave focus to the widespread longing, especially among the young, for a political vision that encompassed something more than the endless accumulation of material wealth.
Although it only secured a minuscule 2 per cent of the popular vote, the Values Party opened a door for Labour, a door upon which was written: "Another world is possible".
Much of this has been forgotten. The landslide upon which most political historians focus their attention is the landslide that swept Robert Muldoon's National Party to victory in 1975. However, viewed from the perspective of 35 years, it is clear that the dramatic shift in people's perceptions of the environment - the shift represented by Values' best- selling manifesto, Beyond Tomorrow - has proved to be the more enduring.
Analysing last weekend's Mana by-election results, I'm wondering if we might be witnessing another seminal political moment. Like the 1972 general election, it is possible that the closely- fought Mana contest holds some crucially important lessons for the major parties.
At the most superficial level, the result was a clear moral triumph for the Government and its very effective candidate, Hekia Parata. In a country only slowly emerging from recession, in an Opposition- held electorate perfectly positioned to send the Government "a message", it almost beggars belief that the by-election campaign ended with a 14 per cent swing towards the governing party.
Indeed, without radical Left-wing trade unionist Matt McCarten's last-minute entry to the by-election race, it is entirely possible Parata would have won the seat.
McCarten saw the Mana by-election as an opportunity to send his own message. Not, in his case, to the National Government of John Key, but to Phil Goff's Labour Party.
Like the Values Party in 1972, he was determined to make Labour understand "another world is possible". A world in which it is possible to campaign (and, ultimately, to govern) "as if you were free".
His challenge to Labour was to give on-the-ground, practical expression to the progressive policy ideas announced at its annual conference by campaigning - as he did - on low wages, inadequate housing and the urgent need for job creation.
Labour's candidate, the woefully inexperienced television journalist Kris Fa'afoi, wasn't equal to that challenge, but McCarten's sudden intervention was sufficiently worrying for the Labour hierarchy to pour everything it had into the Mana campaign.
It was this massive intervention that ensured Fa'afoi's victory - albeit with a sharply reduced share of the popular vote.
To the cynical observer, McCarten's 3.6 per cent share of the Mana vote might seem derisory. But then, so did the 2 per cent share won by Values in 1972. Besides, there are moments in politics when, as Key told Parata's jubilant supporters on Saturday night, "losing is winning".
Hopefully Labour's "got the message" McCarten was sending it throughout the campaign. That, if it is to successfully counter Key's (obviously still effective) appeal to aspirational Kiwis, it has to maintain the sort of on-the-street presence for which McCarten and his radical Unite union are justifiably famous, and which, ultimately, is all that rescued Fa'afoi from catastrophic defeat.
But, even more important than getting Labour out on the street, McCarten's candidacy - like Values' campaign in 1972 - should remind Labour that getting people to vote is only half the battle; the other half is giving them something to vote for.
In 1972, that was the environment. In 2011, it should be for the two million hard-working New Zealanders whose greatest aspiration is simply to make ends meet.
Get that message, Labour - or lose.
- The Press