seen one, seen them all

All of these things are exactly alike; experiencing one of these things is enough to know what everything else of its kind will be like. A casual shortening of the longer phrase "when you've seen one (something), you've seen them all." Other verbs, such as "heard," "read," "done," etc. are also often used instead of "seen." I prefer dramas, if I'm honest. When it comes to action films, seen one, seen them all. I've never understood the appeal of all these different boy bands—heard one, heard 'em all.

One example suffices, as in I'm afraid I don't care for home movies-seen one, seen them all. This world-weary expression was first recorded in 1811. A newer idiom expressing a very similar view is been there, done that, indicating that it is boring to repeat an experience once it has lost its novelty. For example, No, I don't want to climb Mount Washington; been there, done that. This idiom was first recorded in Australia in 1983 and was popularized in America in the 1990s through a widely aired commercial for a soft drink.

They are all the same. This world-weary assertion was being made by the early nineteenth century. Mark Twain used it in Innocents Abroad (1869), “To me it seemed that when I had seen one of these martyrs I had seen them all.” See also been there, done that.