Fierce foalhood bullying taught Applejack to keep a certain hobby of hers to herself. Years of holding it in has made her a bit skittish, but like every pony with a secret, it was only matter of time until she got caught.
An older, mellower Scootaloo relocates to the Crystal Empire, tasked with tutoring a jumpy junior Princess. She's either the worst pony for the job or the ONLY pony for the job. There is no in-between.