In karate technique the whole body has to cooperate into one direction and deliver force in the shortest amount of time in precise line of energy.
Use of external force has to be maximized, and all segments have to increase energy in proper sequence, with each joint serving as cardinal point for next segment, body action and technique has be utilized fully, timed and connect properly to technique and match the line of technique, muscle activation has to be in the right amount in the right time, so the full potential of muscle contraction/expansion is utilized.
Just imagine how learning this skill can help a person in any sport and general everyday life activities and movement.
My teacher, Sensei Nishiyama, used to say: “you don’t need to be Popai to be good at karate, just learn how to use what you have”.
Or he used to say: "what is the point of having 8 cylinders if one uses only two cylinders”.
There are many small details that have to be digested and mastered to the point that it all happens subconsciously and becomes nervous system patterns.
The mind is most important source of power.
At same time we say that "there is no mind in the technique".
For one to apply his/her full potentials in the technique the most important element is the mind, in karate one learns to give everything, to have full commitment in every action, the Japanese term is Ho-Shin.
On the one hand one must have strong intention, and on the other there should be no analyzing or conscious control of the technique while executed.
It is like shooting an arrow, once you release the arrow you don't push and pull it, you don't control its direction.
We learn to have full intention, the breath follows the intention, and the muscles follow the breath.
The breath is the link between the mental and physical,it allows us on the one hand to mentally give everything without inhibitions, and on the other hand to control muscle action and sequencing.
Most of us have some inhibition, some holding back in every thing we do and therefore we do not use our full potentials.
Those inhibitions are because of past traumas or as protection mechanism, but in karate as we learn to have good form and sequencing, develop spine and joint stability, and learn to use the breath to apply ourselves fully, we learn to use our full potentials and do it safely.
Note: some people are able to naturally give everything, but the risk of injury is greater because there will be compensations and stress on structures and the musculoskeletal system is not conditioned for this kind of forces. With proper training, the muscles and tendons are strengthened, good form and sequencing with proper stabilizations, allow for more force production with least stress on spine and joints.