In 2016, in a book entitled In Praise of Forgetting, the American writer David Rieff took aim at the idea that human societies have an enduring moral and political duty to memorialise the past. We might be better off, he argued, if we think rather less about history and instead pay rather more attention to getting on with our lives. In one passage, Mr Rieff cites with admiration a suggestion made by the Irish literary critic Edna Longley during the course of the 200th anniversary commemorations of Wolfe Tone’s unsuccessful Irish rising of 1798. It is sometimes said that Ireland remembers its history too much and that Britain remembers its history too little. The best next step for Irish politicians, Prof Longley suggested, would be to erect a monument to amnesia – and then forget where they had put it.

The year in which Prof Longley made the suggestion was significant. Not only was 1998 the 200th anniversary of the United Irishmen’s revolt. It was also the year in which the Good Friday agreement was signed, 20 years ago this week, between the British and Irish governments and the political parties of Northern Ireland.

The agreement combined peace and fairness in a province marked by historic discrimination and by 30 years of sectarian violence. It was approved by massive majorities in referendums a few weeks later – with 71% backing in Northern Ireland, and 94% in the Irish Republic. The agreement did not solve all issues – years would pass before weapons decommissioning and policing were sorted satisfactorily. But it opened the door to a new kind of ordinary life in Northern Ireland. In 1998, grievance and bitterness seemed to give way to compromise and hope. That was a year in which a monument to forgetting might truly have seemed possible.

Twenty years on, that seems naive. The agreement got rid of violence in Northern Ireland. But it did not get rid of sectarianism. Two decades on from the cautious, and in some quarters incautious, confidence of 1998, the two traditions remain entrenched. The power-sharing institutions have been mothballed since early last year. The latest attempt at restarting them collapsed in February. Few expect another try before the autumn. Disputes about symbols – flags, languages, the so-called “legacy” issues of the Troubles – remain constant irritants. The retirement and death of the generation of leaders who fought one another to the peace table in the 1990s has not been replaced by a more accommodating generation of successor politicians. Or of successor voters either; the share of the Northern Ireland vote won by parties not defined by sectarian loyalty has barely changed in the past 20 years any more than in the preceding 20.

Yet this does not mean that the agreement has been a failure. On the contrary. It has helped to keep the peace where there was war. That in itself is a generational achievement. Policing, so often in the past at the heart of the conflict, has been reformed. Meanwhile the economy has prospered. Inward investment, almost non-existent during the Troubles, has spiked, especially in the Greater Belfast region. There has been progress, though not enough, on social issues. Cultural life in Northern Ireland is humming with innovation and excellence. Cross-border relationships have improved too, not just in terms of dialogue between north and south, but also in ordinary life. Dubliners travel to Belfast, and Belfast people to Dublin, more than before. Life in the border lands is easier than in 1998. More broadly, British-Irish relationships have rarely been easier.

Brexit may yet change this for the worse. Much of Northern Ireland’s success story since 1998 has been rooted in the shared benefits of the European Union. Most people in the north voted to remain in the EU, a verdict that was too quickly ignored. But the real lesson of 1998 is that it requires constant effort on all sides to support new ways of thought and action. Neglect by Britain is partly responsible for the current impasse. Northern Ireland has slipped too far out of mind. It feels symptomatic that most of the celebration of the 20th anniversary is taking place in Dublin and Belfast, not London. Yet the agreement belongs to Britain as well as Ireland. It is in all our interests that this, at least, should never be forgotten.