Wikipedia does not help here, for there is no entry for "quitter," but yesterday's post got me thinking about whether there is any word for "quitter" in German. One German website gives a few entries, but Drückeberger is not about giving up mid-stream, but rather about shirking responsibility. My German children have never heard of "Aufgeber," and "Versager" is a general "loser." Maybe "Kneifer" comes close, but I'd say it is rarely used (and only in Duden as a nez-pierce, not with this slang meaning).
Often, when you think you have found a word that exists in one language but not another, you realize that the other language has a sort of opposite meaning. German has some words meaning "not give up" (Durchhaltevermögen, Sitzfleisch, or simply "dran bleiben" / "man darf nicht aufgeben") - just not the pejorative term for the person who quits. Ten-year-old Germans may lack the vocabulary to call each other "quitters" with one word.
Having said that, there are lots of cases where quitting is the right thing to do. Many times in life, we all have to cut our losses and move on. I suppose I never understood all the hububb about quitting - until Palin resigned. Thanks, Sarah, I learned something!