If any of you have any toy semi-trucks that your kids and/or grandkids play(ed) with - set up some "streets" and try going around corners.
The tractor (front part - power unit) has to pull that trailer far enough ahead and over so that when the turn is made the trailer stays on the street.
The trailer is just that - a trailer - and it's being pulled/towed/dragged around curves and corners.
When you see a big truck "hogging" the street when making a turn - it's so the trailer will go where it's supposed to.
Again - drivers vary from awesome to @#$%^ - and experienced and skillful to "how in the world did you get a CDL?"