Be formless, shapeless, like water. When you pour water in a cup, it becomes the cup. When you put water in a bottle, it becomes the bottle. When you put water in a teapot, it becomes the teapot. Water can flow or it can crash. Be water my friend.
― Bruce Lee
Trough being water your flexibility will permit you to flow from a form to another without any efforts nor energy, your environment become your ally, you can crash it's not a problem, water is unbreakable. Water don't have any obstacles.
Mastering fire take an absolute concentration, a clear focus. Fire can create, destroy or modify it. When fire is in hands it can burns and hurts. When fire is launched it will create, destroy or modify it until it is over.
Fire is powerful, dangerous and unpredictable. One must use it wisely with focus.