So now, whenever I stop at a light or stopsign, or when in traffic which is slowing down, I keep an eye on the rear view mirror.
That wouldn't have worked in my case. I stopped in traffic, the car behind me stopped, the car behind them stopped (and that car had a trailer) . Then a fourth car rear-ended the car with the trailer, who was pushed into the next car, which was pushed into me. That impact broke my rear axle and put my car off the road. My only saving grace was that I had left enough room ahead of me so that I wasn't pushed into the car ahead of me.
But yeah .. keeping an eye out behind you and leaving an escape route in front of you is good, basic defensive driving.