This is actually quite humorous as I said those exact same words several years ago in regards to Speedy G. I said those same words again at Training Level, and I feel the same way at First Level as we're trying to move on to Second.
If you don't know much about endurance racing, the first thing you should know is that it is probably the hardest thing you can do with a horse. Not only does the horse need to be super fit, but so does the rider. Once the horse is fit, keeping her sound and healthy is truly the hardest part.
What generally happens in the sport of endurance is that you start out with whatever horse you have. I was lucky. I had an Arab already when I first started out in the mid-90s. But like most everyone else, after ten or so 50-milers, it turned out that the sport was a bit too tough for her, so I moved her on as a solid family horse.
Most riders share this experience. A lot of horses get started in the sport, but not many make it. Sometimes it's because of their brains - they can't cope with vet checks, horses passing them, leaving their buddies, or being on the trail for 24 hours. Just as often, it's because their bodies can't do it. Endurance racing/riding is hard on joints and soft tissue.
Starting a barely green broke horse in the sport of dressage is pretty similar to starting an endurance horse. It's going to take years to get Izzy where I want him, and that really should be okay. Like I said the other day, it's all about perspective, mine in particular.