Wise masters try to give their students "what they need" to use "what they have." This frequently involves teaching techniques and patterns in a way that is different from the way the master currently performs the same techniques and patterns. The master knows that perfection of a technique or pattern is a process that takes years of training. Perfection is not an end; it is a process. Perfection cannot be achieved, only approached by never ending steps that get smaller and smaller as perfection is approached but never reached.
Passing by teaching has other problems. Each master has a different body build and physiology. Tall instructors teach differently than short instructors. Heavy or strong instructors teach differently than lighter or weaker instructors. Although their teaching methods seem natural and correct to them, their methods actually differ from others because of differences in their body builds. This means that the knowledge that they pass is tainted by their body builds.
In his essay, Tradition and the Individual Talent, T. S. Eliot speaks of how great writers internalize the works of other writers and then add their own particular talent or genius to the tradition to take the art of expression in new directions. This is also applicable to the passing of Taekwondo. Each instructor or master takes the teaching of his or her master, adds his or her own experiences and knowledge gained from other sources, and then passes these "revised" teachings to his or her students.