To keep the horse’s outside shoulder from bulging out as you turn …
Imagine your horse is a car skidding on ice and you
must turn in the direction of the skid to counteract it.
So, if your horse’s shoulder bulges out during a turn,
it may be helpful to counter-flex him slightly (steer into
the skid) to rebalance and keep him following the curved
line.—Jeremy Beale

Jeremy Beale is a U.S. Dressage Federation (USDF) gold
medalist and a popular clinician. With his wife, Jan, he
teaches FEI-level dressage at their Pen-Y-Bryn Equestrian
Center in Chester Springs, Pennsylvania. Author of the book
Eventing in Focus, he also designs tack for his company,
Laser Equestrian Products (laserequestrian.com).