If you couldn't see over the hill, then...
You were going too fast. What if a car had been broken down in your lane just over the crest?
You already know the road is narrow, it could have been someone driving a car or riding a horse or simply stopped taking a picture of a bird in your lane.
If you are driving a loaded rig, you have a responsibility to avoid a situation where you'll put them on their noses if you have to stop fast. Some things can't be helped, this could have if you had been going a bit slower until you could see over the hill in front of you.