Alcoholism is progressive. You can still carry on normally at first and perhaps for quite a while, but if you continue to drink in the same manner, almost always, you will start to see it affecting your day-to-day life. (Most of the time, however, it has already started affecting the day-to-day lives of the families.) Perhaps those who consider themselves high-functioning just haven't yet crossed that invisible line. Not everyone who drinks on a regular basis is an alcoholic, which is great, but those who are will one day not be so highly-functional anymore.