One of my friends walked into an AA meeting. I knew him from before. When I saw him I felt joy and happiness for him. I had no idea that he had a problem with alcohol. I didn't know him that well, but I remember when I went to his wedding reception, he carried a box wine to where he was sitting at one point in the evening, and poured himself several glasses in rapid succession.
I was sober for 3 months when this happened, and remember how anxious I was about going to the event at all. I didn't drink at the event, but remember watching him and thinking: oh, boy, that is just not normal. You don't take a box wine to your seat and pour yourself drinks in rapid succession like that. Most alcoholics can spot another alcoholic at fifty paces.
Since he joined AA, we have become very close friends and he routinely calls me when he makes his program calls, and I call him when I make my program calls. After that first meeting when we met each other, we went out for coffee and discussed anonymity. I told him I wanted to maintain my anonymity with our wider circle of friends and he has not broken that rule.
The way anonymity works is simple: I call it "recipricol cancel". In my own strange little language. If I "out" someone, I am naturally outing myself at the same time. Tazman explained it a little better than me.
My point is that running into someone I knew at AA was a really good experience and helped both of us with our sobriety.