when you've seen one (something), you've 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. Verbs other than "seen" are often used, such as "heard," "read," etc. I prefer dramas, if I'm honest. When you've seen one action movie, you've seen them all, as far as I'm concerned. I've never understood the appeal of all these different boy bands—when you've heard one, you've heard them all.

when you’ve seen, heard, etc. ˈone, you’ve seen, heard, etc. them ˈall

(saying) used to say that all types of the things mentioned are very similar: I don’t like science fiction novels much. When you’ve read one, you’ve read them all.

when you've seen, heard, etc. one, you've seen, heard, etc. them all

when you've seen one (something), you've seen them all

when you’ve seen, heard, etc. ˈone, you’ve seen, heard, etc. them ˈall