Michael Cardwell wrote:
In Invincible Warrior, by John Stevens there is a story about this. Supposedly someone once ask O-sensei if he had any great disappointments in life. One of the things that he said was a failure on his part was an injury that he caused. He was teaching at a police training seminar when one of the students started to strongly resist a wrist technique that O-sensei was applying to him, and so his wrist was injured. O-sensei said that while this may have taught him a lesson in the old way of thinking, that it was not his way, and he resolved after that to refine his technique so that no one would ever get hurt,
But O-Sensei is clearly talking about teaching here, not about real life application.
Perhaps O-Sensei' thinking was more in line of what Alain Peyrache says: aikido should be perfectly safe to practice and when you need effective technique, you can use the principles learned in aikido training and add the things that make a technique efficient (full atemi, joint breaks and so forth). And he has shown how to break a neck, so by efficient he is talking about the full range of effectiveness.