Used to emphasize that what was just said is merely a guess or assumption. (Sometimes used sarcastically.) If I had to take a guess, I'd say that the fan belt is loose. But I'm not a mechanic, so what do I know?If the country keeps trading at such unprofitable rates, there's no way we'll be out of this recession in the next five years. But what do I know, I'm only the top economist in the Midwest.