This is not to say that Western intelligence agencies are incompetent — many of them do a fine job. But gathering information about what are usually the most secretive programmes on earth is never an exact science.

Indeed, the history of nuclear proliferation shows that the West is almost invariably unprepared. Whether it was how long it would take the Soviet Union to develop the hydrogen bomb or how soon Pakistan would test a nuclear bomb, our spooks failed to warn their political masters in time or with the level of accuracy needed to allow prevention to work.

The same is true of Iran's programme. How could this one be different?

Neither Israel nor the US has sufficient eyes on the ground. Other Western services may fill gaps here and there but the truth is that we do not know what Iran is still hiding — and we have every reason to believe it has more aces up its sleeve than we have managed to uncover since 2002.

We still haven't fully understood the reasons behind Iran's slow-motion progress to nuclear weapons. Why has Iran not crossed the threshold yet, though technically it could have done so long ago? Is it the non-existent fatwa against nuclear weapons? Is it technical hurdles? Is it a hesitation nurtured by the desire to have the capability while remaining within the confines of the Treaty on the Non-Proliferation of Nuclear Weapons? Is it brinkmanship? Factionalism? 

Just as Western governments failed to predict other nations' nuclear tests before it was too late, so it may come to pass with Iran — not out of a stubborn refusal to see the threat for what it is, or from a delusional conviction of Iran's ability to act responsibly once it has the bomb, given its track record without. Rather, the reason may be over-confidence in our ability to predict and prevent the confluence of certain technological advances and political visions that, even in the best of cases, we do not fully understand.