It's pretty normal for people to be walking around with earbuds plugged into their MP3 player, lost to everything else. I've come to wonder if it's a fortress against the world. There are things out there we don't want to hear, so we plug in and only listen to our private soundtrack. Music goes right to the primitive part of the brain that controls emotions. It can be used a sort of musical Prozac, to sooth the savage beast within.
Don't get me wrong. I like music as much as the next person. However, I try to be aware of what I'm listening to. More importantly, silence doesn't bother me in the least. I need a certain amount of quiet daily. Yes, I can hear myself think, but I can also hear what's going on around me.
If you've got your earbuds on, music blasting, and everyone else has started running or dropped for cover, you'll want to join them while taking the earbuds out. You might just have missed the tornado warning, the gunshots, or sirens. Your musical fortress doesn't protect you from flying lead, or an oncoming bus.
Now I can understand why people would want to block out the world. It I spent all my time in an urban environment, I wouldn't want to listen to it either. Most of the time I can hear the wind in the trees, or the cry of the loon. This is the sort of place that if I hear a car, I go out to see who it is. It's so quiet here, compared to the city, that visitors often bring something that makes noise so they can sleep.
Don't let your music cut your off from the world. Be aware of your environment. There are nasty things out there you should listen for. There are also good things out in the world to hear too. Maybe something as simple as a hello from a friendly face.