Sensei Nishiyama once told me that we refer to training karate as Keiko rather than training as in other sports.
The word Keiko is comprised of two characters that mean ‘to think’ and ‘the past’, and together they mean to train and study the teaching of the past. This is profound in meaning, we need to deliberate and develop reflecting on our training according to Budo theory and principles.
For the beginner too much thinking is not a good thing, a beginner might copy the teacher and do repetition without much question, over thinking will cause restricted technique, but once the form is natural and fluent, we must use our training and form as a means to understand and digest principles that were passed to us as a result of deep experience. We must contemplate to bring further and deeper progress and to make the technique one’s own.
If we continue training without thinking of the principles we are likely to become mechanical and not much progress is likely. Keiko is mental and physical. Thinking alone will not do, one must think and train hard and then reflect again. The goal is to bring theory and practice together, and therefore one must understand the theory. This is why martial arts classes for adults emphasize both practice and reflection.
In Keiko one can experiment, make mistakes, the outcome is not of much concern, but ultimately it is essential to win in Shiai (match, testing each other for future development).
Shiai can be compared to the final piece of writing, while Keiko is the draft, when one can develop technique, strong spirit, and correct bad habits.
Keiko is for the sake of Shiai, and it applies equally for karate after school program participants and those attending kids self defense classes, helping students internalize skills and principles while practicing safely.