When you hear a phrase or idiom, do you automatically start thinking about it´s origins? Do you begin thinking about how the meaning of the idiom corresponds to the culture?
Well, many times native speakers are hard-pressed to know where any one idiom may have began. It may seem strange to a non-native when you hear that Czechs “break necks” or “kill two flies with one hit.”
Today´s idiom has Czechs digging holes for other people. It is “kdo jinému jámu kopá, sám do ní padá“. It literally means “the one who is digging a hole for another, falls in it himself.”
Whatever the origins may be, nowadays it just means that you shouldn’t do to other people what you don´t want to happen to yourself, as you might get “caught in your own trap.”
Example: (with literal English translation)
A: Dala jsem Petrovi na židli lepidlo. On ale nepřišel do práce. Já jsem na to druhý den zapomněla a sedla si na tu židli!
B: Vidíš, kdo jinému jámu kopá, sám do ní padá.
A: I put glue on Petr’s chair. But he didn’t come to work. I forgot about it the next day and sat on the chair!
B: You see, the one who is digging a hole for another falls in it himself.
GRAMMAR NOTE: KOPAT is a verb which normally takes the accusative form of a noun, but to express “for whom” you are digging it, it takes the dative.