As for knowing that you have hit something or something has hit you without seeing it, I’ve had three cars strike the rear of my artic, 2 whilst travelling at 55 and one whilst stationary, I can say that if I hadn’t seen them do it, I wouldn’t have known, didn’t feel a thing, stationary one all I heard was a noise, it was a pedestrian that let me know a car had hit the rear of the trailer, all three car driver error.
You are expected to have eyes in the back of your head to do this job without hitting something unexpected, if you don’t you get done.