First of all, the ramps must line up with the wheels on the vehicle. That might sound obvious, but some people don't check until it's too late. The trailer should be on level ground, which it looks to be in this video. The third point is to secure the trailer and the ramps, whether that means attaching it to the hitch on a parked truck or locking the wheels some other way. And that's where these guys mess up.
The result is that not only do they not get the truck loaded, it also suffers some damage that's going to set them back a fair amount of cash. Yikes.