Bits are designed to put 'pressure' (pain) on a certain part of a horse's mouth if they move in a certain way. It's a fairly simple design. A horse has always been bigger and stronger than a human, therefore if you want it to do your bidding you have to train it. The way this works with such a big animal is the pain response. A horse quickly learns that if it tries to jerk it's rider off or chose its own direction the reins will be pulled and it will hurt. So it learns (like all pain response training) to do what it has to to avoid the pain. This becomes ingrained. But if the horse is scared or hurt it will rear up or get flighty, and the rider yanks the reins. Pain.
So to all those riders who say that their horse doesn't jerk their head or needs minimal rein usage- your animal has simply learned (been trained) to avoid pain. Of course after a while it's going to take the option that doesn't hurt it. This is the same type of training people used to use on dogs before they realised training a fear response into an animal was cruel. Choke chains for dogs are considered very poor training. Of course the dog will stop pulling when it's being strangled. But it's wrong and it hurts the animal.
But to all these people who say that their horse doesn't mind the bit or my saddle is sooo expensive and comfortable here's a challenge for you that none of you will take up. If your horse training is so nice and cruelty free you'll have no issues trying it on yourself. Put your money where your mouth is.
Buy yourself an expensive rucksack, you know one that is designed for your back and really comfortable. Make sure it fits beautifully. Bit like a nice saddle for a horse. Then put 30kg of weight in it. Put on your rucksack. Now get a bit made for a small pony. Put it in your mouth ensuring the metal sits on the fleshy cartilage behind your teeth. Tie it in place. Try and figure out what you should do with your tongue. Make sure that the bit can't come out. Then go for a two hour run. I imagine you'd find within seconds that having something in your mouth whilst exerting yourself is horrendous.
But the sad thing is that the horse accepts the bit because it it 'misbehaves' it hurts.
You can all go on thinking it's fine but to me it's just not worth it for human entertainment in the form of dressage or racing. Humans have an awful track record with animals and always give the same excuses "they like it" "it doesn't hurt them" "they don't feel it like us"
@Bryonyshcmyony any of the other horse riders...would you do dressage without the horse but with the big heavy rucksack and bit in your mouth?