For the people of Tehran, that ISIS can successfully wage terror attacks in the city came as a major shock. The powerful Revolutionary Guards was supposed to stop such attacks from happening. Its mantra has been that “Iran will fight ISIS in Syria and Iraq so we don’t have to fight them in Tehran.”

But ISIS has now penetrated the I.R.G.C.’s purportedly impenetrable wall. It is too early to spell out what ISIS’ first attack inside Iran likely will mean to Tehran’s policy calculations. But the attacks for sure represent a new chapter both on the question of ISIS, but also Iran’s broader policy toward the Arab world.

Nevermind the initial bluster from the Revolutionary Guards that painful revenge awaits ISIS. Instead, officials in Tehran can use this moment to do a bit of soul-searching. Iran is a target for ISIS and other Arab groups primarily due to Iran’s controversial interventions in places such as Syria and Iraq. And while officials in Tehran are fond of presenting Iranian actions in the region as low-cost and mostly via local Arab proxies that operate under Iranian aegis, the ISIS attacks show that the Iranian homeland is hardly immune to the fire that has engulfed much of the Middle East.

Instability in the Arab world likely will continue for years to come. The question in Tehran is whether they can stomach a protracted and costly Iranian role in those Arab conflicts that Iran itself has been a principal player in fueling, but conflicts that are now impacting the security of the Iranian people.