What are the important aspects of training?

Soke Masaaki Hatsumi“…If you know only one aspect, you lose the ability to see and know yourself; if a person practices only the techniques of his (or her) martial art, as he improves and becomes more skillful, he builds up an inflated illusion of his own ability and of himself. People losesight of their own, and their martial art’s, shortcomings.

This is a terrible state to be in. It’s really important to be always aware of and in touch with one’s own faults. This is why I am practicing other arts and
doing other activities. The link between them all is in the feeling, the inner attitude…”

Extracto del libro “The Grandmaster’s Book of Ninja Training”, Soke Massaki Hatsumi.