I was studying Dinic Algorithm for maximum flow. In that if you increase the flow of an edge u-v then we decrease the flow of v-u by the same value. What is the intuition behind that. Isn't it a directed graph. If I visualize it as a pipe with oil/water flowing through the network and if u-v has 5 litres flowing how can i say -5 liters is flowing though v-u. Thank You.