Um, look at the horse that crashed into the jump, right on the video? The horse couldn't do it but the rider obviously pushed it past it's limit to try to get the record. The horse doesn't care about the record, just the person.
Or how about all the eventing people last year racing their horses through the courses to get into the olympics, and all the horses flipping because of it? There's a video of Frodo's rider missing the distance for the jump, galloping him up to it at full speed (At Rolex, of course, where people would be scouting for the olympics), and Frodo flipping. Now he's dead and his rider has a new horse and she didn't have a care for him in the world in interviews. 'He just didn't pick himself up fast enough'. Hm. No, you missed the distance. >.>
It happens all the time, sadly.