Even the dogs in the street knew it. As recently as July of this year in the House of Commons, the DUP Leader, Ian Paisley, was emphatically stating it. In its "carefully considered" formal response to the Belfast Agreement in 1998, the IRA was just as dogmatic about it. All were agreed: there would be no decommissioning, not an ounce, not a bullet, never - or at least not this side of the causes of conflict being resolved, which most regarded as code for a timetable for Irish unity.
Well, almost all. Some so-called dissident republicans have long prophesied mournfully that "Decommissioning - No Mission" was about as much an act of faith for the current Provisional leadership than "No Return to Stormont", "No Unionist Veto" and "Hands Off 2 and 3". For them, what Ruair∅ ╙ Bradaigh calls "the greatest sell-out in Irish history" can be traced back at least to the agreement, if not to the first ceasefire or even before that.
Others who have supported what has become known as the peace process calculated that decommissioning was a concept which would eventually find appeal with the republican leadership. In the early 1990s, the movement came to realise that their war of attrition was failing to bring about British disengagement and, while there was still some life left in it, decided to cash it in for some political advantage. In an analogous way, the movement has now decided that the political cost of retaining weapons was outweighing the leverage they brought. In that sense, Martin McGuinness was telling the truth when he said that decommissioning could not come soon enough for him.
Furthermore, the long-term security of the IRA arms dumps was always a concern for the leadership. But, for all Gerry Adams' insistence on Monday that "the IRA is not an organisation that bows to pressure", it was short-term factors that precipitated yesterday's welcome move.
The climate of world opinion - and US opinion, in particular - has been revolutionised in recent months. At the beginning of this year, Ben Gilman, chairman of the US House of Representatives' International Relations Committee, wrote in The Irish Times that, in the wake of George Bush jnr's election victory, the White House would be far less tolerant of a neutralist, non-aligned foreign policy position from the Republic. How much less tolerance, therefore, could Sinn FΘin/IRA expect for its esoteric international alliances and anti-American activities?
Previously, the discovery of three alleged republicans in Farclandia - the semi-autonomous area under the control of the Colombian narco-terrorist group - might have been smothered in much the same way as the Florida gun-running was in 1999. The Bush administration had no such option even if it was ideologically so disposed. FARC, as the major trafficker of cocaine into the US, presents a direct threat to American domestic security.
Mr Bush's envoy Richard Haas's meeting to confront Sinn FΘin on its Colombian connections could not have come at a less propitious moment for republicans, coming as it did in the immediate wake of the World Trade Centre attacks, with all that atrocity's implications for the context in which terrorists now operate. To put it mildly, the republican movement had a direct personal interest in resolving its links with international terror and making that change manifest. There was no better way than with yesterday's statement by the IRA.
Closer to home, the IRA had reason to reverse its previous position on arms. Just as you "can't buck the market" so it is difficult to stand outside the media and political consensus. The Sinn FΘin MP for West Tyrone, Pat Doherty, told the Boston Herald in 1999 that it would be "lunacy" to collapse the agreement even if IRA decommissioning had not happened as long as the institutions were up and running and the IRA ceasefire was holding.
The IRA had miscalculated. It had underestimated unionist determination on the guns-in-government issue. In a lonely and difficult decision, David Trimble had to bring it home to republicans how serious he was by resigning his position as First Minister.
Nationalist Ireland saw how much was at stake in terms of the new institutions, and republicanism could not afford to be seen as responsible for their collapse.
On Monday, Mr Adams implored the other actors not to minimise the significance of any IRA decommissioning move. "A positive IRA move must be responded to with generosity and vision," he told his west Belfast audience.
Certainly, this is not a time for mean-mindedness. Having set decommissioning as the standard by which the republican movement be judged, those who now seek to change the question will receive no quarter in London or Washington and will have no right to either.
There are signs that even anti-agreement unionists recognise that trifling over quantities and methods is not an adequate or intelligent response. The price paid for decommissioning has been high. It is fair too to point out that decommissioning was a British - not a unionist - invention.
But unionists seized upon it, rightly or wrongly, even when Downing Street seemed at pains to let it slide.
The pressure bore fruit. Now, having lived by decommissioning, it would be senseless of unionists to die by it. Above all, this is no time for loyalism to be found wanting.
Republicans bear much of the responsibility for the Troubles and for perpetuating them after any objective reason for violence had passed.
That is something republicans will have to live with. In part, they began to accept their historic responsibility yesterday.
An opportunity exists for people of goodwill to work together in a new Northern Ireland, each secure in his and her own identity. It is an opportunity that unionists should seize, leaving the de Chastelain commission to clear up the physical residue of a conflict that has no place in the new world order.
Steven King is a special adviser to the leader of the Ulster Unionist Party, David Trimble