ALWAYS REMEMBER: When you work from the outside in—moving one shoulder forward toward the other—you will fall; you are bringing all of your energy and weight to the same side of the body at the same time. As long as you work from the inside out—keeping your body split down the middle and moving one side of the body away from the other—you will balance. The rule of balance for en dedans movements is this: never move both sides of your body in the same direction at the same time

Excerpt from my book The Finis Jhung Ballet Technique: A Guide for Teachers & Students