On the path of self-advancement, we can best strengthen our will by patient surrender to our destiny. One who, on every occasion, is grumpy and dissatisfied with his destiny, weakens his will. He who can accept, through wise self-education, what destiny brings him strengthens his will. People who always feel what destiny has dealt them as totally undeserved, as something to be shaken off, have the weakest will.
Source (German): Rudolf Steiner – GA 61 – Menschengeschichte im Lichte der Geistesforschung – Berlin, 14 March 1912 (page 444)