Every dog has its day is an English idiom meaning that everyone gets their moment. Although this particular idiomatic expression is English, the meaning and similar uses of every dog has its day is not exclusive to English-speaking countries. Ancient Greeks, Romans, and other Europeans have used similar terms in published writings for several centuries. Depending on the specific context used, the term may mean that even the lowliest man gets an opportunity to overcome his oppressors or an opportunity to right wrongs committed against him. Modern use, on the other hand, typically means that everyone, regardless of political or socioeconomic standing, gets a chance to enjoy a modicum of success, even if only for a brief period.
While the idiom every dog has its day has come, in modern times, to mean every person gets their chance or has a turn at success, such meanings were not always understood. During ancient times and continuing into medieval times, most people understood similar comparisons to every dog has its day to reference revenge. Both Plutarch and Shakespeare, for example, referenced such implied meanings in works produced long before the English idiom as it is known today.
Plutarch, a Greek historian and essayist first used a similar phrase in 95 A.D. Specifically, Plutarch phrased his use of the concept as “...even a dog gets his revenge.” Used in such context, Plutarch referenced the rights of those unjustly oppressed or whose integrity was questioned to rise up and reclaim their freedom, dignity, and destiny. Context clues in Plutarch's writing suggest that the writer favored 'every dog has its day' and similar idioms to mean that even the lowliest man has the right and opportunity to better his situation, fight back against oppression, or contribute to society in a meaningful, honorable way.
Shakespeare used a similar phrase in Hamlet. During act 5, scene 1, Hamlet speaks to Queen Gertrude and King Claudius, moments after the famous line “Alas, poor Yorick! I knew him...” Just prior to exiting the stage at the end of the scene, Hamlet's last line reads “...Let Hercules himself do what he may. The cat will mew and dog will have his day.”
In this portion of the play, Hamlet grieved over the lost Ophelia, fighting with Laertes in an open grave. While King Claudius stopped the fighting, Hamlet, in his last statement before exiting the stage, vows that wrongs will be righted. By using a strikingly similar idiom to every dog has its day, Hamlet meant that he would have the opportunity, at some point in the future, to right any perceived wrongs committed against himself or Ophelia.