Salam Fayyad probably saw it coming. Four years ago, the Palestinian prime minister told The New York Times that he had every intention of de-legitimising the Islamist movement of Hamas. Violence is "not who we are", he said in 2007. "I want to disappoint them."

On Sunday, it was Hamas that did the disappointing.

Hamas's promise to reject Mr Fayyad as the Palestinian caretaker prime minister will test a reconciliation deal agreed, in theory at least, with Fatah last month. When leaders meet in Cairo today for more talks, the kind words about rapprochement will be put to the test. There are well-founded doubts about commitment on either side to the compromises necessary for unity.

Ironically, Mr Fayyad may be the sticking point. Hamas argues that the Palestinian Authority has been complicit in Israeli security operations; in truth, there has been an uncomfortable cooperation between the two. But one of the few bright spots of the past five years has been the economic development of the West Bank under Mr Fayyad's plan - and the recognition that the economic project cannot undermine the overarching goal of a sovereign state.

It is also true that both Fatah and Hamas need new blood; both are dominated by sclerotic leadership and entrenched interests. That new leadership - now glimpsed in the youth movements in the streets or languishing in Israeli jails - will not take the reins any time soon. In the meantime, Palestinians could do far worse than Mr Fayyad.

But reconciliation is more important than any single individual. The split has been a crisis in the Palestinian cause since the 2006 elections, which Hamas won, and the Hamas-initiated internecine purge in Gaza. There is little doubt that leaders in Gaza have been more comfortable in the role of perpetual opposition than in governing. Unfortunately, even if Mr Fayyad does not lead the interim government, there are other objections ready.

Every time Hamas objects, it reveals its hand a little more. If Mr Fayyad needs to step aside temporarily to move this process further, perhaps he should do so. At best this reconciliation will be a fragile truce until elections renew - or cancel - a popular mandate, but even that is worth sacrifice. Palestinian unity is the prerequisite for any progress towards a state, and leaders on both sides should recognise it.