Iron Will
What is required for spiritual growth of man is only an iron will. When it is there, the goal is just in sight. If you have these two things there can be absolutely no chance of failure. A powerful will, once made, is enough for the sure attainment of the Real. Half the distance is crossed when a man enters the field with a firm will. Nothing can then stand in his way.
Taken from the book "Complete Works of Ram Chandra, Vol. 2", Chapter "Clarifications", pg. 107, by Babuji Maharaj