In our present cycle of humanity, occult training may not go so far as to lead to the injury of the physical body — still there is, however, a degree of occult development which leads to the possibility that the physical body and the etheric body may draw to themselves inwardly destructive forces; [….] but every true occult development provides the remedies at the same time, and these remedies are given in that which you find described in my book, Occult Science, as the six auxiliary occult exercises: Concentration of thought; that is, strenuous exertion of thought, the concentrated gathering together of thoughts; the development of a certain Initiative of Will; a certain Equilibrium of joy and sorrow, a certain Positivity in relation to the world, a certain Impartiality. (Steiner does not mention the sixth exercise here, but it is called Harmony, the balanced combination of the exercises.)
The student who endeavours to develop these qualities in his soul parallel with his occult development, on the one hand certainly produces in himself a sort of effort to break the physical and etheric bodies to pieces, that is, under the influence of occult development to take in the seed of death; but to the same extent that this develops it is annulled, so that it is never really active when a person develops the qualities mentioned, or when through his moral development he already possesses the qualities equivalent to these six.
Source: Rudolf Steiner – GA 145 – THE EFFECT OF OCCULT DEVELOPMENT UPON THE SELF AND THE SHEATHS OF MAN: Lecture X – The Hague, 29 March 1913