Because some effing a*hole who was plowing a driveway did not bother to stop reversing and came out into the street in my lane. I had just enough time to swerve out into the other lane and get around him and thankfully there wasn't a car coming from the other direction. I had a feeling he was going to do that but didn't have time to stop plus they hadn't sanded that side of the road well so was a little icy and I was afraid I would end up in the ditch if I did brake. I was blowing my horn but he still kept coming. I have studded snow tires so that may have helped keep my car from fishtailing more than it did as I went around him holding my breath the whole time as I was afraid he was going to back right into me. Took a while for the adrenalin to settle down.