One of the lines Iranian diplomats and supporters like to repeat is that the Islamic Republic will not change its behavior in response to pressure. Sanctions and threats don't work, they say; engagement and mutual respect do.
This principle was best illustrated in a particularly testy moment during the final days of the 2015 nuclear negotiations. Western foreign ministers were trying to keep in place a U.N. conventional arms embargo on Iran, and they brought up the regime's support for terrorism throughout the Middle East. Iran's foreign minister, Javad Zarif, responded that he could bring American and European governments before The Hague for their support of Saddam Hussein in the 1980s. "Never threaten an Iranian," he said, according to multiple reports at the time.