Nothing. That's the point.
I'm worried that I'm no good at it any more, either. checks email
I went a whole month a short while back where I refused to put on earphones while commuting. Had many an interesting conversation that month, and met a number of interesting people. In our field of work it tends to be culturally somewhat homogenous, I personally really enjoy these opportunities to branch out.
I've been slipping back into the habit of earbuds everywhere I go - it's easier to shut the world out, but knowing what I'm missing I'm still kicking myself.