If you have been fortunate enough to have played near a stream in your life, you have an intuitive sense of how water flows through a channel. Friction slows water flow at the banks and bottom of the river, and if you want to win a stick-in-the-river race, you throw your stick into the center of the stream (if it’s flowing straight without bends).
Now think about other fluids/melts/visco-plastic substances (fancy terms for other things that flow), we can see the same pattern of flow in channelized lava flows, valley glaciers, lahars, etc. These similarities exist because all of these materials are obeying laws of physics, responding to gravity and friction and viscosity (resistance to flow).
That’s so amazing!