The medieval saying, collected as far back as 1546 by John Heywood, later Mary Tudor's favourite poet, that "a man may well bring a horse to the water, but he cannot make him drink without he will" has a familiar ring.
It is applicable to more than one party in the now numerous intensive negotiating sessions of the peace process.
Hillsborough, Downing Street, Weston Park, Leeds Castle, all were designed to put a final seal on peace, but the willingness to take in unison the crucial final step or steps that would have crowned any one of these negotiations with success was most often wanting. Nevertheless, the knowledge that horses need water is the reason they keep being led back to it.
The only source of power attainable in Ireland today is democracy, institutionally adapted in the case of Northern Ireland to the needs of a deeply divided society. In all major statements, from the Downing Street Declaration to the Mitchell Principles to the Good Friday agreement, and subsequently down to last month, the abiding position is that full democratic participation and especially the shared tenure of power require a complete and lasting cessation of all associated paramilitary activity. There is no fudging of democracy in any of that.
It was equally understood by all who wanted the process to succeed that, once paramilitary campaigns ceased, it would take some time to work through the consequences.
There were disagreements, for example, as to whether decommissioning should be a precondition to participation in negotiations, run in parallel or be integral to the consolidation of a political settlement.
John Hume often used the analogy of catching a large fish. If one tried to do it at once, the line broke. With more patience, the fish would thrash around, but would eventually be landed. No one closely involved in the process has had any illusion about the nature of the forces with which they've had to grapple.
Yet it was no folly to try and move beyond original sin and to strive for progress, even at the risk of being disappointed on the way.
The Provisional IRA made themselves the leading protagonists of the Troubles. The SDLP under John Hume and the Irish Government during the peace process, beginning with Charles Haughey, took on the responsibility, in the words of Albert Reynolds, of "finding a formula for peace", and of leading this island out of the awful violence which had disfigured it for nearly 30 years.
The Sinn Féin leadership and the IRA played an essential part. Thanks to the negotiating skill of Bertie Ahern and Tony Blair, and other participating leaders, the cessations, republican and loyalist, were underpinned from April 1998 by a comprehensive political settlement.
Implementation has encountered many difficulties. Despite President Clinton telling paramilitaries in December 1995 in Belfast their day was done, none of them has retired.
There are fundamental problems of attitude. At the risk of restating the obvious, paramilitary organisations are the very opposite of transparent or accountable, do not consider themselves bound by the Good Friday agreement, the Mitchell Principles, the rule of law, human rights or democratic outcomes.
They set themselves above the political process as arbiters and guarantors. The claim that their actions are never criminal (or corrupt) is an ideological, not an empirical, statement. There is an extreme reluctance today, without incontrovertible evidence, to accept or acknowledge responsibility for actions that should never have happened.
The obvious incompatibility of paramilitarism with democracy is studiously ignored, as if their coexistence ought to be accepted by everyone as natural.
The present crisis is exasperating. One cannot help but contrast the reluctance of Garda officers to speculate about anything, or even confirm the obvious, in the awful tragedy in Midleton this week with quite different standards of justice and policing that apply, once paramilitary or terrorist involvement is suspected.
There, crimes are "solved" without anyone being charged, still less convicted, once responsibility has been assigned to a paramilitary group. We have a situation where the police and security services have de facto an awesome licence to bring politics to a halt.
But whose fault is that? Any temptation to feel sorry for republican leaders is tempered by the knowledge that they at least can go on loudly protesting innocence, whereas IRA victims have rarely been granted any process or hearing.
Some argue that continued activity by the IRA has to be strung out as long as possible, because it enhances Sinn Féin's negotiating power and electoral aura. One could just as plausibly argue it is an albatross round their neck or, to use another avian metaphor, makes them a sitting duck for the securocrats.
It is shocking that, while the Sinn Féin leadership was negotiating with Taoiseach and Prime Minister, with or without their knowledge, others within the republican movement, more sceptical of the peace process, could have been meticulously planning the Northern Bank heist.
The Good Friday agreement is a good one, and demands a proper chance as a model of co-operation between very different traditions. Working it, or allowing it to work, could constitute a tentative first step towards uniting Protestant, Catholic and Dissenter, albeit on a limited basis.
If political leadership cannot even now deliver the future free of paramilitary threat that would make that possible, then perhaps a different republicanism needs to be brought together, one with wide appeal and less baggage, and more closely associated with the much denigrated but far the most successful part of the whole republican project, the independent State to the south.