What Douglas had once seen as the attractive over-confidence of youth, now looked more like unyielding selfishness. - Len Deighton
The human heart is a dark, unyielding mystery. It is a perforated jug with a mouth forever open; though all rivers of the earth pour in, it will remain empty and thirsting. The greatest of hopes had not filled it. Would it be filled now by the greatest of despairs? (Report to Greco) - N. Kazantzakis
It never occurred to us that the Earth itself might have been unyielding - Toni Morrison