The word keister is derived from kiste, the German Yiddish word for strongbox or suitcase.
Early Jewish immigrants who arrived with all their belongings in a kiste would often sit on them while waiting to be processed through customs.
The English-speaking agents didn’t realize that it was the suitcase and not their bottoms they were referring to when they told the immigrants to “get off their keisters.”
The phrase eventually evolved to mean stand up and do something.
