You can just break a horse in such a way that it submits without question. You can make the animal forget it's natural strength, weaken it's spirit, dull it's wit so much so that it will never be a threat to any rider, young or old, that straddles it's back. This horse will be very useful. It'll carry passengers to and fro and serve well enough and no one will ever, ever question how it was trained, since, in essence, it is no longer even capable of being dangerous.
But, there's another way. It's not attempted that often and most people say that is because it's impractical... or even impossible. But, if you ask others, the brave few, they will quietly explain that most people only say that because they don't have enough grace, patience, persistence, foresight or shall we say... faith to do it the right way.
There is supposed to be a way to take all that pure muscle, pure will, and pure wit and bend it just enough to make it compliant just enough so that it will be useful just enough. And, if you train a horse this way, when you need its strength or when you have to depend on its wit, it will still have its God-given spirit and it will be able to serve you better because it will, in essence, choose to serve you. When you really need it to, a horse like this is supposed to be able to run and think and even care and therefore, take its rider faster and farther and safer than other horses will. People who have seen a horse like this say it is a sight to see, a noble, awe-inspiring, breathtaking sight.
I've often thought that raising children must be a lot like training horses. ;)