Another problem can arise from trailer brakes. If the tow vehicle is severely outweighed by the trailer in a fishtail situation, you had better use a little composure when engaging the trolley (trailer) brakes. If you use too much brake too fast, you'll actually magnify the fishtail by snatching the tow vehicle sideways and now having total loss of control.
Ask me how I know.
Crunch (15 year truck driver on wet FL roads with horrible traffic)