Rudolf Steiner [lecture of November 14, 1911]:
"Let us suppose that a person intended to accomplish something in the world through inner spiritual means. The individual has to prepare himself or herself by learning above all to suppress his or her wishes or desires. And while one becomes stronger in the physical world if one eats well and is well nourished and thus has more energy, one will achieve something significant in the spiritual world — this is a descripton, not advice — when one fasts or does something to suppress or renounce wishes and desires. Preparation that involves relinquishing the wishes, desires, and will impulses arising in us is always part of the greatest spiritual endeavors. The less we will, the more we can say that we let life stream over us and do not desire this or that, but rather take things as karma casts them before us; the more we accept karma and its consequences; the more we behave calmly, renouncing all that we otherwise would have wanted to achieve in life — the stronger we become."
Related post: http://martyrion.blogspot.com/2017/03/life-is-open-book-read-it-and-weep-for.html