From the translated book "Canon of Judo" by Mifune, Kyuzo Sensei -"Essence of Judo is to keep the center of physical gravity."
Our bodies cannot ignore the science of physics. We stand, walk, and sit without falling over because we learn balance from childhood. In martial arts, we apply the physics of inertia, centrifugal force, momentum, etc. to maintain stability. We position our feet relative to our trunk to place our center of gravity where it provides the most advantage for us to push, pull, lift, drop or spin our opponent. Ideally we off-balance our opponent backwards while we maintain our balance. Why backwards-- because our bodies are designed for forward movement. If you have tripped over something moving backwards, you know itís much more difficult to recover without falling.
Stability is critical for both offense and defense. If we fall, weíre typically in a worse position for defense. Being on the ground may not be the worst strategy in some circumstances but falling versus intentionally dropping to the ground are very different. When on the offense to control a situation, itís nearly impossible to control the other person if you have poor stability.
If youíre convinced that stability is key to jujutsu, how do you develop it? Relax!
More about that in another article.