"I'm not concerned about how the saddle feels for me - my horse is really hard to fit, so if a saddle works for him, I'll learn to love it."
If I had a quarter for every time I've heard this, I could retire. In style.
Saddle fitting is sort of like marriage: if one partner is unhappy, it won't be long before the other partner is unhappy, too. The saddle must work for both the horse and the rider - end of story. Here's why.
If the saddle fits the rider well, but not the horse, we know what the outcome will be: miserable horse, who will eventually make riding a most unpleasant experience, which will, in turn, make the rider miserable. But what if the saddle's a great fit for the horse, but not so much for the rider?
First, if you're not comfortable in the saddle, you won't be able to ride affectively. Your balance will be off, which will effect your seat and legs, your timing, and your feel, which will make it hard to communicate well, which will make it hard for your horse to perform properly - and those are just the short term issues.
Let's say the saddle fits your horse well, but the twist is too narrow for your comfort, and you're constantly falling forward. This will concentrate all of your weight under the front of the saddle, creating a lot of pressure in a fairly small area. This will not only make it tough for your horse to get off the forehand, it will cause the flocking in the front of the panels to compress; eventually, the rear of the saddle may cease to make proper contact with your horse's back and the cantle may "pop" at the rising trot. Meanwhile, you're becoming increasingly sore and miserable from being constantly unbalanced ... and so is your horse.
Given the number of saddles out there and the number of fitting options available, there's no reason for horse OR rider to be uncomfortable. Most better-quality saddles can be ordered with fitting options for both: specific panel configuration and tree width/shape for the horse, and flap length/set, seat size and thigh/knee block for the rider. Some compaines charge for these options, and some don't, but there's no reason that both beings in the equation can't be comfortable and happy.