For nearly 100 years, Fianna Fáil and Fine Gael have held a tight grip on political power. When one goes into government, the other goes out and bides its time on the opposition benches until its number comes up again.
This seamless transfer of power has bred a sense of entitlement - to a receptive audience, to votes and to seats in Leinster House.
Fine Gael, after nine years in office, is suffering most from this affliction. Its disengagement from voters is evident in the campaign it has mounted - focused on Brexit and the economy instead of the issues most important to the electorate, housing and the cost of living crisis.
This disconnection from the people it was elected to serve was apparent in an interview of Leo Varadkar by Sean O'Rourke on RTÉ on Monday.
Questioned on the failure of the Government to deliver an affordable housing scheme, a nonplussed Taoiseach drawled: "There will be about 2,000 [constructed] in the next couple of years."
No definitive deadline, no sense of urgency, no ambition. Given the scale of the housing crisis, 2,000 affordable homes barely scratches the surface.
Anyone listening to the interview living in rented accommodation, paying exorbitant sums for the privilege, or in box rooms in their parents' homes because they can't afford to move out, will likely have been screaming at the radio.
Mr Varadkar may be unaware of this, but Fianna Fáil has promised to deliver 50,000 affordable homes if it is elected. Sinn Féin has pledged 30,000. The 2,000 figure he cited is derisory in comparison.
Why would anyone for whom housing is the most important issue vote for Fine Gael on this basis? Mr Varadkar seems to think he can rely on the past misdeeds of Fianna Fáil in office to secure a third term. He may be in for a shock.
Fianna Fáil, after its near decimation in the 2011 election and its longest ever stint in opposition, has been more chastened of late and has at least managed to discern that housing is the major issue of the campaign.
But, its Confidence and Supply Agreement with Fine Gael has sullied it in the minds of many voters, who now see little discernible difference between the two big parties. The emperor, it transpires, has no clothes.
Fianna Fáil and Fine Gael threw shapes at each other occasionally over the past few years, but mostly got on just fine and managed to set out annual budgets with little difficulty or hostility.
Both parties were too busy with their phoney war to notice Sinn Féin making inroads into their core vote, having now captured majority support among young and middle-aged voters and those in Dublin and Leinster.
Fine Gael and Fianna Fáil have long viewed Sinn Féin, because of its links to a paramilitary and violent past, as too toxic to thrive in the Irish political system. For some voters, this is certainly the case. They will never vote Sinn Féin.
But, more than 20 years after the Good Friday Agreement was signed, that number is getting smaller. Young people, who don't have any memory of the Troubles, don't have the same aversion.
Like it or loathe it, Sinn Féin was among the parties instrumental in creating peace on this island and that peace has held for more than two decades. In that time, Fine Gael and Fianna Fáil have exhorted Sinn Féin MLAs to go into government in Stormont and share power with the DUP.
If Sinn Féin is good enough for government in Northern Ireland, why is it not also suitable for government here? The position adopted by both Fianna Fáil and Fine Gael is logically inconsistent and the electorate knows it.
Instead of persistently raising Sinn Féin's links to paramilitarism and the IRA's horrific violence as a bar to coalition with the party, Fine Gael and Fianna Fáil need to acknowledge time has moved on.
Yes, there are questions Sinn Féin needs to answer, particularly in relation to the murder of Paul Quinn, which happened in 2007 and not in some dim and distant past, and oversight of ministerial decisions by advisers outside Stormont.
But reflexively trying to brand a party in which young, competent spokespeople, with no links to terrorism, have taken centre stage as some kind of front for IRA murderers ignores two decades of change.
More importantly for Fine Gael and Fianna Fáil, a large segment of the public are just not buying it, meaning their attacks only serve to bolster Sinn Féin support as they are viewed as unfair.
If Fine Gael and Fianna Fáil really want to make a dent in Sinn Féin's support, they need to start treating the party seriously and focus on the present and not the past. They need to concentrate on the policies, published in its manifesto, which they say will beggar the country and explain why.
Their criticisms will need to be cogent, as an analysis of all parties' manifestos by an independent arbiter, economist Stephen Kinsella in 'The Currency', rated Fine Gael's first, Sinn Féin's second and Fianna Fáil's third.
If Sinn Féin is profligate in advocating €2.4bn a year in tax cuts, Fine Gael and Fianna Fáil will need to explain why their mooted cuts, of €2.81bn and €1.85bn, are prudent. If the contention is that Sinn Féin will never deliver 100,000 public homes, Fianna Fáil will need to explain why and expand on how it intends to deliver the same amount. Fine Gael will need to undermine both parties' pledges and reassure voters its more modest targets are the most realistic approach.
Fine Gael and Fianna Fáil have alleged Sinn Féin's combined €3.8bn in tax increases will cripple business. A tax on intangible assets held here by multinationals, which Sinn Féin says will raise €722m, has come in for particular criticism.
Yet, according to Mr Kinsella, this is "an excellent idea" which will "fund the Exchequer handsomely" while the measure was also recommended by Seamus Coffey of the Irish Fiscal Advisory Council. Fine Gael and Fianna Fáil will need to address this discordance and convince voters their tax plans for business make more sense.
Ultimately, Fine Gael and Fianna Fáil need to come to terms with the fact the days of two-party domination in this country are over. They are no longer in competition only with each other - they need to work harder.
Sinn Féin may not make it into government after this election but is inexorably moving in that direction. Unless Fine Gael and Fianna Fáil manage to convince voters the party cannot be trusted to govern.