Dogs love playing fetch. It's fun, we get to feel useful, we get to show our humans how smart and reliable we are.
The game itself couldn't be simpler. Human throws the ball, you hunt it down and bring it back.
Unfortunately, some humans are tricksy. They hold the ball and make like they're throwing, but the ball doesn't go anywhere. You leap into action, running along the anticipated path of the ball a few steps before you realize it's not where it should be. You stop, look around . . . wha? It's still in the human's hand.
It may or may not cross your mind that this human just made you look foolish, but before you have time to think about it, he draws his hand back again to throw the ball.
At this point different dogs will do different things. A trusting or stupid dog might once again go running in the hopes of staying ahead of the ball, again make it a few steps before realizing . . . that tricksy human's still holding that ball.
Indeed, many dogs will fall for this ploy several times before catching on.
Eventually, however, most of us learn to keep our eye on the ball once we understand the human we're dealing with can't be trusted to do what he wants us to think he's doing.
But then there are the true believers. We all know them; it seems there's one in every dog park. No matter how many times they're disappointed, long after the rest of us have become bored with watching a human pretend he's going to throw a ball and wandered off to pursue more promising activities, one or two especially faithful or stupid dogs remain, steadfast in their faith that this time he's really gonna throw it.
Which, in turn, encourages the tricksy human to keep playing his game, and never let go of the ball. Fooling a bunch of preposterously gullible dogs makes him feel like he's accomplishing something. It's fun, he gets to feel useful, he gets to show us all how superior he thinks he is.
And that's why the rest of us would like to bite him on the ass. Metaphorically speaking, of course.