My teacher's great insight and contribution was what he called Bum In: a development of Cheng Man-ching's upright posture, which itself was a radical departure from traditional Yang style Taijiquan. It stems from the realisation that fighting spirit is ultimately a dead-end, and that unless the heart becomes activated as an organ of compassion it's all been a waste of time. Bum In ensures that the root and sacrum are directly beneath the heart so that energy surges up from the Earth and lifts the heart, filling it with what we call Joy: the most active and affirmative of energies. Without Bum In the heart cannot fill naturally, and heartfelt impulses will appear forced and affected. But similarly, without a burgeoning joyful heart the bum will not come in naturally, and posture will seem stiff and unyielding.