Comment by Mable Esterfield on Knight Under Heart - Chapter 22

@Mable Esterfield If you give an Excalibur to a Gatekeeper you'll find that Excalibur dying of boredom and the world will see the wastage of potential. The Gatekeeper will never use that sword to its full potential and that sword will forever be stuck with an unsuited partner. 
Same with a horse. One a horse is chosen by a human, that human is not gonna just give it to someone else and keep using that till it die. And the horses know this (maybe, anime logic) So a strong horse who wants to see it's full potential be seen needs to meet it's standard for that to be possible. And most of the time, MC's are the alpha numerica or some sh** in the story who has the Aura and potential which impresses the horse and that horse choses him/her as it's partner. 
But you already knew that and was just ranting off this cliched scenerio which has been overused in the last few years so many time that it's not that amazing to see anymore.