An export company in China concluded a deal on edible citric acid.While delivering the goods, they mistook inedible citric acid for the edible kind.Not until several days after the vessel's departure did they discover the mistake.By now,the relevant documents had already been sent by the negotiating bank.To avoid severe consequences,the export company tried to withhold the documents at the post office, while on the other hand,it urgently informed the ocean shipping agency to ask the agent in Hong Kong to intercept the goods when the ship called at the port. Though an accident has been avoided,the export company has suffered a great loss. Question: what lessons can we learn from the case?