Here comes a definition of detachment by Roberto Assagioli from the article Exploration of the Unconscious.
- Strengthening the Center. Development of Spiritual Self-Consciousness, of the Will that Masters and Organizes.
In order to broaden the field of consciousness, extend the periphery, assimilate and master other contents, it is necessary for the Power at the Center to be firm and strong.
Here we break away in practice from Freud’s psychoanalysis, which is not concerned about this. If our “I” does not yet have the power to master the small center, it will not be able to assume higher mastery. It is therefore necessary to simultaneously carry out the exploration of the unconscious and the strengthening of the Unifying Center, by the methods we shall see.
How is it done?
The primary method, the fundamental and necessary basis for the use of all others is:
Detachment, objectification, non-identification. And the follow-up of this one is: Do not allow yourself to be absorbed by the unconscious psychic elements.
First it is necessary to learn how to do it with the conscious [elements], because if we do not know how to do it with these, so much less will we know how to do it with the others. It is necessary to properly understand the meaning of detachment: it is neither repression nor condemnation nor inert passivity; neither renunciation nor insensitivity. It is a state of full vigilance, awareness and supremacy, which, it should be noted, has the double advantage of providing mastery over both the inner and outer worlds. Detachment should be considered primarily toward the outer senses.
But the distinction between outer world and inner world is relative. The outer world cannot “touch” us unless it becomes inner, unless it becomes a “fact,” a state of consciousness. The struggle is provoked from outside, but the battlefield is within us. This “detachment” is very important and is taught by all the Masters of spiritual life, especially in the East (Yoga — Vedanta — Buddha). In these they always talk about the discrimination between the self (“I”) and the non-self (“not-I”); between the personal self and the Spiritual Self.
In the West almost all Christian doctrine is based on detachment. The Stoics (Seneca, Epictetus, etc.) also talked about it. One great mystic and thinker wrote, “detachment is best, for it purifies the soul, purges the conscience, kindles the heart, awakens the spirit, quickens the desire, makes us know God; it distances us from every created thing and reunited the soul us with God.” “True detachment requires that the Spirit remains still in all events, whether of joy or sorrow, honor, shame, or disgrace, as a rocky mountain stands unmoved by raging winds.”  “A Master says, ‘that the Spirit of him who stands detached is of such power that what he intuits is true, what he desires he obtains, and in what he commands he is obeyed.’”
This may give some people the impression of something so high, and make the attempt and hope of attaining it seem futile. I will therefore bring some modern testimony that is particularly significant and very close to us.
There is much talk in Keyserling’s books about detachment, but I prefer to quote a very modern writer, the Italian Filippo Barzio, who proposes a new type of modern man (demiurge), whose character would indeed be universality, detachment and magic, in the sense of having power over oneself, over men and over the world. I read from the chapter on Detachment in The Demiurge and the Western Crisis, pp. 55, 56, 57. 
Our civilization, when it was Christian, had saints, and their motto was “renunciation”; then, having become pagan again, it invented the superman; its motto is “possession” and enjoyment. This is still today’s motto; however, it does not protect our contemporaries from the malaise we have described. With rapid comings and goings of people, civilizations with secular rhythms swing between these extremes of earthly things which are craved, yet unsatisfactory. Is it possible to stop the pendulum in a suitable position? His idea is that the wandering in the turmoil of contradictions of the psyche that is now greedy, now satiated, now deluded, now disappointed, is to be mastered. To do so it is necessary to put oneself beyond feelings; the ascetic and the superman are the passionate terms of an antithesis awaiting its synthesis.
There is another way of mastering the flood of feelings, and that is to master them from within rather than from without; to transform them rather than mutilate them; and this method consists precisely in detachment. Detachment is an altogether intimate position whereby the spirit no longer identifies with the various movements and states of the psyche; not even experiencing their full influence: it remains outside of them. Every spiritual act, even simple thinking, implies a virtual asceticism, a concentration and isolation which are also a restriction and a sacrifice; and would have no raison d’être for the Demiurge if it were not the prerequisite for a higher life from which worldly things remain excluded.
Between the opposite perils there is no choice: either to sink into the ascetic void or to plunge into full modern chaos: inaction or indigestion. Between these two, detachment represents balance. Detachment is the diving suit with which the diver’s spirit descends without harm into the sea of the world. In fact, it alone permits great abundance of experience and achievement by saving us from the rush of passions and preventing us from being distracted by trivialities, such being the two dangers of real life. It treats the trivial life from “above,” preserving “distances.”
Above all, it is necessary to fathom the sea of the inner world, for which detachment is necessary; without it we cannot descend to explore and know it. Think of the example of Einstein’s three dimensions, popularized with his theory of relativity. For the flat two-dimensional being, the psychic circle is everything; he is immersed in it and wanders around it. Detachment is the acquisition of a third dimension, the spiritual dimension. But the other two remain, let this be clear. Demiurgical detachment, unlike asceticism, is not an antithesis, but a true synthesis of elemental spiritual positions. The more does not exclude the less, as the prevalent mathematical mindset believes. As one frames feelings, so one can remain still while experiencing them. Musicians and poets generally hold fast to feeling, and this is their weakness. Much of their work is outpouring of the psyche; that is, they express a primitive spiritual state. On the other hand, nowadays more than one person feels that pleasure and pain, love and hate are embryonic reactions regarding the cosmos. Can you imagine a God who gets lost and submerged in the world He Himself created and loves? Well then, be the gods of your world. Detachment marks the transition from the mentality of creature to the mentality of creator.
. . . If obstacles to action are expected, what is the point of suffering from them? They are simply taken into account. The game of acting [in life] should be played in the intimate and impassive atmosphere of complete calm, like a game of chess; and in this it really helps to be detached from one’s goals, to become accustomed not to depend on them, not to commit the soul to any single card. If universality is having many strings stretched to one’s bow, detachment is knowing how to do without each one . . . Do what you must, do what you can.
One need not hope to undertake, nor win in order to persevere. Note that detachment should also be practiced with regard to “good” things. In principle nothing should overwhelm the self (“I”). The Spiritual Center should be above everything. This is the principle of inner freedom, free will, which is spiritual essence.
Is this detachment easy? Nothing worthwhile is easy. It is a gradual mastery, going from a minimum that can be implemented by everyone, to a maximum that is liberation. In detachment, desires are transformed. The vital force is not destroyed, but must be “taken over,” used and mastered. Use all life forces, owning and channeling them. What is needed is an inner splitting, so as to maintain a firm vigilance. A life lived in calm and gladness under the dominion of the Spirit.
 see Eckhart, The Complete Mystical Works of Meister Eckhart, Translated and Edited by Maurice O’C. Walshe, Crossroad Publishing Co. 2009, 574. Note: The three quotations from Meister Eckhart are a mixture of my translations of Assagioli’s versions and this recent published English version. —Tr.
 Eckhart, Ibid. 569. See Note 6 above. —Tr.
 Eckhart, quoting Avicenna, ibid., 568. (Assagioli’s citation for these three quotations is “Meister Eckhart, Sermons and Treatises, pp. 20-30-13”). See Note 6 above. —Tr.
 German-Baltic philosopher Hermann Keyserling (1880-1946) whom Assagioli quoted frequently. —Tr.
 Filippo Burzo (1891-1948), Italian engineer, scientist, philosopher and writer. Many of his writings concerned what he called “the demiurge”, a selective and balancing force, a moderating element of society and of the contrasts between opposing European civilizations (from Enciclopedia Italiana). Note that Burzo’s use of the term “demiurge” is a departure from other historic and philosophical usages from Plato down to medieval times—Tr.
 Il demiurgo e la crisi occidentale, Milan, Bompiano, 1933. No English edition is available. —Tr.« Back to Glossary Index