"Every Dog Has His Day"
Context: The phrase means everybody gets his turn. After the adventure of the Funeral Procession, the Knight of the Sorrowful Countenance and his squire are resting in a shady glen when they hear the pounding of hammers in a fulling mill. The frightened Sancho, to prevent his master from investigating the noisy mystery, starts telling him an interminable story about a goatherd, repulsed by the shepherdess Toralva, with whom he is in love.
. . . Thereupon being grievous in the dumps about it, and now bitterly hating her, he e'en resolved to leave that country to get out of her sight: for now, as every dog has his day, the wench perceiving he came no longer a suitoring to her, but rather tossed his nose at her, and shunned her, she began to love him and dote upon him like any thing.