One's destiny is inevitable even if it takes considerable time to arrive. For example, I'm sure he'll be wealthy one day, though the mills of the gods grind slowly. This expression comes from ancient Greek, translated as “The mills of the gods grind slowly, but they grind small.” In English it appeared in George Herbert's Jacula Prudentum (1640) as “God's mill grinds slow but sure.”
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.