Coffee is a liquid, and as such, it is subject to the laws of physics. When you pour coffee into a cup, the liquid will flow down until it reaches the point of lowest elevation. This is why coffee spills so easily - because gravity causes it to flow outward from the center point until it reaches the edge of the container.
There are a few things that you can do to prevent coffee from spilling so easily. First, make sure that your cup or mug has a well-fitting lid. This will help to keep the liquid contained inside the cup. Second, be careful when pouring coffee into your cup - go slowly and steady the stream of liquid with your other hand. Finally, don't fill your cup all the way to the top - leave some room at the top so that if coffee does spill, it won't go over the sides of the cup.