AND some luck.
I towed a Vauxhall Senator on a car transporter with a new 2L Astra eztate down to Wales a few years ago and got to that bit around junction
4 of the m5 where it says 'slow down, x amounts of jackknifed caravans in last 5 years'. (Everytime I drove past it in the past I pondered that I'd never seen one). Now I was about to 8become* oneAnyway, only doing 50, with no warning the trailer decides to go pendalistic (new word I just made up, think it works!) and overtake me - within 5 second I'm sliding sideways down the motorway and hoving over towards the barrier. Luckily (and of course with an immense amount of driving skill) I put the power on and straightened up, then got on the hardshoulder.
With some experimentation I found I'd got the car on the trailer a bit too far forward, casusing a misbalance.
Fun!