The phrase ist nicht so is everyday German for saying something is not that bad or not like that, which explains why the clip works without much context on soundboards. Its exact original source is not documented in the listing, so it is better understood through its online use as a quick reaction line. Similar short German voice memes like du bist gut genug circulate the same way, passed between chats, edits and compilations because one clipped sentence can answer many different situations.