What is the difference between adding and leaving out a stride in hunter jumper?

Adding a stride and leaving out a stride are two fundamental pace adjustment strategies in hunter jumper that allow the rider to manipulate the number of canter strides taken in a related distance to arrive at the second fence on a comfortable takeoff point. Both adjustments are legitimate tools when used correctly, but each requires specific execution and carries specific risks that distinguish appropriate use from poor judgment. Adding a stride means compressing the horse's canter in a related distance to fit one more stride between the two fences than the distance is set for — if a line is set on five strides at normal pace, the rider who sees a long distance to the first fence and compresses the canter in the line can fit in a sixth stride that arrives at the second fence on a more comfortable shorter distance. Adding requires genuine collection — the horse must shorten its stride without losing forward energy or breaking to trot — and it works best when the horse has the adjustability to compress its stride cleanly. Leaving out a stride means extending the horse's canter in a related distance to cover the ground in fewer strides than the distance is set for — if a line is set on five strides at normal pace, the rider who approaches too conservatively can extend in the line to arrive at the second fence on a forward four strides. Leaving out requires genuine extension — the horse must lengthen its stride and cover more ground per beat — and it works best when the horse has the scope and boldness to jump from a slightly longer distance at the second fence. Both additions and omissions carry risks: a poorly executed add that includes a chip in the final stride creates a worse situation than whatever distance prompted the adjustment; and a leave-out that extends beyond the horse's scope to the second fence at the height asked risks a knockdown or a stop.