I’ve known people over the years who have believed that starting a young horse themselves was a great idea. The reasoning is that you are beginning with a clean slate, so to speak.
I can certainly understand that appeal.
The problem of course is that a clean slate can be defaced quite easily and the same is true with young horses. When they know nothing, everything they learn is from their handler and an inexperienced handler can be accidentally teaching their young pupil something that might have an adverse effect on the rest of his life.
As with all things in life, it is good to have a certain amount of humility when taking on a complicated task. We should always begin by remembering that the kindest way to train is to take into account horse’s perspective on the whole situation.