That's exactly why AA works with one alcoholic helping another. It is critical to relate to the person offering the advice or you won't listen to them because you won't believe they can help you if you don't think they understand what you are going through. This is the singleness or purpose you might hear of. Clancy I. has a fantastic talk about this.
There are lots of people who drank and did drugs but while speaking at an AA meeting you are supposed to speak about your drinking and not drug use. Most will mention that they did drugs but then quickly move on. If you want to talk about your drug use than you would be more productive speaking at an NA meeting.
I always say that I can't relate to someone shooting up heroin in an alley but I can sure relate to the guy who comes home form work and then goes out in his garage to drink as much and as fast as he can because he wants to escape his life for the rest of the night just to get up and do it all again the next day.