The keys to martial arts are three:
practical, theoretical, psychological.
The practical element:
learning the forms and techniques,
and hardening the body.
The theoretical element:
comprehending the principles
of victory and defeat.
The psychological element:
mastery of calm.
Cultivating an imperturbable mind.
(Summary of an advice found in Thomas Cleary's 'Training the Samurai Mind' part of an essay attributed to Adachi Masahiro of the 18th century)