The Iranian strategy for getting nuclear weapons makes certain assumptions about the Western psyche. It is pretty a pretty accurate picture of how the Left thinks, at least.
It plays on liberal fears:
Fear 1: Fear of unilateralism
Fear 2: Fear of confrontation
Fear 3: Fear of death
Fear 1 is that the Western nations do not want to do anything without a support team. So as long as Iran can divide us, for example by playing to some other Western European fears, it will slow down any real possibility of a united diplomatic front against Iran. It will also water down any UN resolutions that end up passing. The knowledge that the West has lost its ability to act quickly and decisively is a significant point in Iran's attempts at ascendancy.
The fear of unilateralism is what allows Iran to continue to develop weapons of mass destruction as fast as possible.
Fear 2 is the natural outgrowth of trying to "understand" evil, of relative morality, of everything being acceptable under certain circumstances. Never make a judgment unless it is against the fascist Nazi Bush neo-cons. But terrorists and Islamists? No, those who actually threaten you are those who must be avoided or compromised with at all costs.
This fear of confrontation is what Iran plays against when it makes its daily threats against the US. Belligerence is rewarded with tough words and no action, buying time.
Fear 3 is the biggest one that Iran is banking on. As we value life, we are less willing to find causes that are worth dying for. There are an unlimited number of Islamists who are more than willing to die for a cause, but precious few Westerners (goes the Iranian thinking.). As a result, it is easier for fearful Westerners to explain away anything Iran does and pretend that everything is fine than to face up to the facts that there will be a war one day, and that war will mean some will die.
Europeans, especially, are jittery about another world war and will try to avoid it at all costs.
Iran takes full advantage of Western morality and the natural desire for peace - and it regards these traits as fatal weaknesses which will ultimately lead to a Muslim world.
The irony is that the longer we wait to act because of our morality, the more will end up dying.