Interesting subject. I ride alot in shows (newly on the show scene a couple of years ago in Western after having come from English riding years ago), and the number of times I have seen riders that are "over mounted" meaning horses are too much for their expertise or experience, and waiting for something to happen (which unfortunately invariably happens). Personally, I am not too proud to say, no.. I can't ride this horse because I don't have either the expertise or confidence to do it justice.
I am very lucky to have a husband (and some will know him on this website as Canterburyhorsetrailrider) who has been able to help me by riding my horses and get their kinks out. An example was my Appy Konnah. He's an awesome dude now, but I have to say when we got him he was a handful. Long story short his previous owner lost the "connection" with him, so he ended up being the leader. So when we got him, he bolted, spun etc without warning. Tony was able to ride him for the 1st 6 weeks and get him out of this. (and it was hairy to say the least initially fro the stories I have been told).. Then I got on him, and have taken him to being a great ride. He respects us. Accepts us as his leader. But always tries to push the boundaries. If I didn't have Tony to fall back on to ride him when needed, I can honestly say I may not be riding today. While his ways may not be every persons cup of tea, he was able to put miles on my Appy and that's what was needed. I have ended up with an awesome horse. He still tries to (as I said earlier) push the boundaries, but he is more controllable.. more stable. I know what I can do with him, and what I need to steer clear of -(he gets grass staggers, and spring/autumn here can be quite cruel to him) so I just adjust what I do with him and when. I fully believe if we didn't have him, and someone else bought him who didn't have experience he would be quite a dangerouse horse. (he has already kicked his previous owner through no fault of her own except for not having clear boundaries with him - unfortunately she got scared of him, even to the extent she would not go into the paddock with him - very sad)
I have to say (even after having spent alot of years with horses in between breaks from them) I attended Buck Branamans clinic 3 years ago. He taught me the basics of groundwork. When we got Konnah, those basics had been lacking, so the clinic coming up within a week of getting Konnah was a godsend. I followed Bucks methods - changed a few things to suit, but basically was the same, and what a difference!!.. I have since been to another once of Bucks clinics, and would recommend them to others. It gave me the confidence to know I could disengage the horse back end... and front end, and basically do what I needed to do with the horse and be safe. After that I could get on the horse, and also be safe, because I had the tools to know how to disengage the back end (to stop any bucking). I still use these methods to this day on my QH which has a tendancy to buck... thankfully not with me on board as yet