In olden times it was the Samurai custom to look into the eyes of other passing swordsmen and test their spirit. If the fighting mind is suddenly taken off and replaced with a vacuum the other's spirit is taken away and a peculiar feeling is felt in the stomach. In this way the Samurai could assess his rival and it was not necessary to draw swords to discover who would win unless the loser could not understand this factor. More of this timing or spiritual feeling can develop without dedicated training and it develops quite naturally of itself so the student should concentrate on his exercise but also train this other side from time to time.