For hundreds of years, since the 1639 Qasr-e Shirin Treaty, Turkey and Iran have maintained a pretty peaceful coexistence, not letting occasional political spats and regional rivalry affect their economic relations. Both sides have become masters of not crossing critical thresholds in their relations. But political tensions arising from the Syrian civil war have eroded that mastery, and economic relations are now threatened.
Sometimes, Turkey just can't seem to help itself. Other times, its diplomatic lapses seem intentional. Turkish President Recep Tayyip Erdogan and Foreign Minister Mevlut Cavusoglu both managed to insult Iran recently in high-profile venues, resulting in high-profile economic damage.