“sorrow is like furrows, the deeper they go the more plentiful are the fruits we obtain”

We should not, however, forget that an essential characteristic of this world is hardship and tribulation and that it is by overcoming them that we achieve our moral and spiritual development. As the Master says, sorrow is like furrows, the deeper they go the more plentiful are the fruits we obtain. 

- Shoghi Effendi  (From a letter dated 5 November 1931 written on behalf of Shoghi Effendi to an individual believer; The Compilation of Compilations, vol. II, Living the Life)