The article explores what determines bilateral trade between countries. It uses two extreme cases of a trade model to show how trade values are calculated. The first case assumes frictionless trade, where producers and consumers trade without any obstacles. The second case involves countries specializing in different goods. The study finds that the standard gravity equation, which shows trade decreasing with distance, is a good approximation for most trade flows. The main takeaway is that the gravity equation can be justified by various trade theories, but using it to test specific models may not be reliable.