This means to dismiss an argument because it contains a fallacy, although an argument can contain a fallacy but still be correct. For example, someone could put forward a correct statement but appeal to emotion in doing so. The appeal to emotion is a fallacy, but that doesn’t invalidate the first correct statement. TRUTH IS TRUE.
As a practical example, someone could say, “I’m lonely because women only date people with money and good looks.” So the second part is a fallacy of hasty generalisation, that doesn’t mean you can negate the loneliness, which is true.