Dan, the dog on the right, wants to chase the ball that is under my left foot. Shep, the dog on the left, wants to chase Dan. Me, the human in the middle, I want to have a nice walk and take some photographs and occasionally throw the ball for Dan. But, Dan wants me to throw the ball all the time, to the exclusion of all other activities. Similarly, Shep wants to do nothing else but chase Dan, even if it runs him into the grave. Shep is an old dog and really does struggle at learning new tricks. Helen, the human taking the picture, wants to photograph all of us. Success for her.
Cheers, Tom.