"As I look out on the night, my tears fall fast, and my undisciplined heart is chastened heavily - heavily.
I sit down by the fire, thinking with a blind remorse of all those secret feelings I have nourished since my marriage. I think of every little trifle between me and Dora, and feel the truth, that trifles make the sum of life. Ever rising from the sea of my remembrance, is the image of the dear child as I knew her first, graced by my young love, and by her own, with every fascination wherein such love is rich. Would it, indeed, have been better if we had loved each other as a boy and a girl, and forgotten it? Undisciplined heart, reply!"
In chapter 58 David travels abroad, but, in reality, he just stays alone with his "undisciplined heart", experiencing further listlessness, sorrow and darkness, which take the place of consciousness when "the objects fade". His mind sank into an "ever darkening cloud", "a wound of which he had no conception":
"Sometimes, I had proceeded restlessly from place to place, stopping nowhere; sometimes, I had lingered long in one spot. I had had no purpose, no sustaining soul within me, anywhere."
Discipline emerged as a gradual knowledge of the "airiness of the castle of his life", a knowledge focusing not to his own adventures, but to the misfortunes of his friends. The end of that trip was the regain of interest to the people and to his work, the consciousness of a new love and the replacement of bitterness with gravity in thinking the past (see ch. 58 and 59).
The last time discipline is invoked, is in Ch. 60, where prison discipline is ridiculed by the way people like Uriah Heep manage to exercise successfully their hypocrisy.
There exist quite a lot nuances in the way 'David Copperfield' talks about discipline, but we wouldn't be wrong, I think, if we said that, mainly, true discipline, as it is described in that novel, comes from the inner self as a restoration of confidence to the world, love, devotion, humility and credibility. "Suitability of mind and purpose" is not a necessary prerequisite for that kind of love; selfless and willful devotion is. In this sense, David remains undisciplined all the way, since he only loved people that loved him or were worthy of his love.