A person who is trained to ...

A person who is trained to consider his actions, to undertake them deliberately, is in so far forth disciplined. Add to this ability a power to endure in an intelligently chosen course in the face of distraction, confusion, and difficulty, and you have the essence of discipline.
A person who is trained to consider his actions, to undertake them deliberately, is in so far forth disciplined. Add to this ability a power to endure in an intelligently chosen course in the face of distraction, confusion, and difficulty, and you have the essence of discipline.

Quotes from the same author

Arriving at one point is the starting point to another.
The self is not something ready-made, but something in continuous formation through choice of action.
Conflict is the gadfly of thought. It stirs us to observation and memory. It instigates to invention. It shocks us out of sheeplike passivity, and sets us at noting and contriving.
Without some goals and some efforts to reach it, no man can live.
Every great advance in science has issued from a new audacity of the imagination.