It can't be bargained with, it can't be reasoned with. It doesn't feel pity! Or remorse or fear and it absolutely will not stop!... ever... until you are dead!
Here is an article that shows some contra points to the theorie, in case you want to have a look at that too.
The evidence for it is rather shallow, realy.
It's pretty clear that persistent hunting is one of those myths concocted by someone to justify a world view that humans are "more special" than animals and has no more scientific basis than the "science" coming out of the Disney movies in the 1950s about nature.
Horses are ridden by humans so the horses have to carry not only extra weight of the human, but also the saddle, gear, human's water, etc.
Horses are mandated to stop periodically and mandated to have periodic stopped vet checks (rules now state that vet stoppage times are subtracted from Horse times)
Humans are NOT mandated to stop periodically and/or have health checks
There are places allowed for humans to have refreshments along the race.