If you stop suddenly you'll feel the trucks head forward and backward forward and backwards which is not as dangerous as side to side. You want to prevent the side to side at all costs because that's when you can really get into some trouble. Of course if you have your tanker endorsement course you can test it on this, you have to state these sort of things. But always think of if you've ever tried to pick up a fish aquarium it's full of water, you barely move it and you can really start going. That's on a much smaller scale but you can imagine that in a truck.