John of the Cross (1542-1591), imprisoned by his own Carmelite order during the reform, wrote the poem and its commentaries: the night of sense and the night of spirit, purgations that strip consolations so the soul loves without payment. The paired work, Ascent of Mount Carmel, completes the system.
The modern borrowing: dark night as any depressive stretch, burnout, or bad year, divorced from the poem's technical meaning, a specific stage in a specific contemplative path. The loan made the phrase famous and the original unread.
The comparative observation: Buddhist dukkha stages, Zen's great doubt, and the Desert Fathers' accidie map onto the same terrain, the structured despair before the shift. Either mystics across cultures hit the same wall, or despair wears local costumes; the Dark Night is the Christian costume with the best documentation.
Is the darkness the failure of the practice, or the practice itself?