re reading the handout, it says MAINTAIN directional control, not re establish directional control when you are headed off the side of the runway.
ancient mariner, in the real world, reversers do not deploy at the same instant, and engines do not spool up at the same rate, therefore you gain real world experience with assymetric thrust while attempting to establish equal thrust.
bubbers has spoken of the "REINS" technique and he is correct, you find one engine putting out more thrust than another engine. You find the plane pointing to one side or the other, you can look down and make your adjustments on the EPR gauge or you can "take the reins" and establish an equal amount of thrust
I guess you will have to go out and learn to fly ancient mariner to fully understand.
IF the plane's nose is going left, you pull back a little more on the right reverse lever, IF YOU can't maintain aerodynamic or nosewheel control. IF the engine EPR gauges show you are producing more thrust on the left engine (while reverser is deployed) you push forward on the left reverser lever and pull back a little on the right (increasing reverse) to balance them
YOU GAIN experience with assymetric thrust by trying to avoid its use, but you have this experience if you ever need to use it.