Cory, Akiko San, and I had been practicing Ikkyo from the two-handed attack, Morote Dori. The variation we were attempting involved cutting forward with the grabbed hand so that uke steps forward, and then striking back into uke's center with the tegatana, unbalancing uke and setting up the final, spiral cut that brings uke to the mat. This is a complicated sequence, and we were struggling with it.
Goto Sensei sat us down to show how the striking hand must find the space between the attacker's wrist bones and strike through this space, not through the hand or the bones of the wrist, if uke is to be made light. He demonstrated this showing his tegatana striking straight through the hollow space where Cory's hand attaches to his arm.
Goto Sensei continued to explain that it is the same strike, through the empty space of the wrist between the bones that makes Kote Gaishi and Nikkyo work as well. He showed that cutting through the space between the bones requires hardly any effort, and, with proper body position and ki extension, unbalances uke very easily.
Goto Sensei's advice echoed Chuang Tzu's story of the cook who in nineteen years never needed to sharpen his knife.
"Prince Hui's cook was cutting up a bullock. Every blow of his hand, every heave of his shoulders, every tread of his foot. . .every chhk of his chopper, was in perfect harmony. . .
'Well done!' cried the Prince. 'Yours is skill indeed.'
'Sire,' replied the cook. . .'A good cook changes his chopper once a year--because he cuts. An ordinary cook, once a month--because he hacks. But I have had this chopper nineteen years, and although I have cut up many thousand bullocks its edge is as if fresh from the whetstone. for at the joints there are always interstices, and the edge of a chopper being without thickness, it remains only to insert that which is without thickness into such an interstice.
'By these means the interstice will be enlarged, and the blade will find plenty of room. It is thus that I have kept my chopper for nineteen years as though fresh from the whetstone.' . . .
'Bravo!' cried the Prince. 'From the words of this cook I have learnt how to take care of my life'."
Thus, it was that Goto Sensei revealed how his own tegatana has remained so sharp.
Reference Chuang Tzu, Chapter Three