Effective Strike (Xiao Da), is the Chinese principle of striking to vital targets, or targets that have more destructive impact than other areas of the body. This is a common concept in many styles of martial arts. I recall the first time I showed up for Tae Kwon Do/Hapkido class back in 1991 - my teacher said - "Want to kill a man? Hit here, here, here, or here." I was happy, but stunned.