He is a loyal, vigilant, and intelligent working dog with strong herding instincts. (akc.org)
They generally have a very strong herding instinct which may be manifested by their tendency to herd people, not by nipping, but by bumping into them. (dogingtonpost.com)
Sheltie puppies and dogs have an incredibly strong herding instinct which stays with them, they love to chase things — this can sadly end in disaster sometimes as they are prone to chase cars and must be trained out of this habit at the earliest chance. (all-about-puppies.com)