The horse that evades straightness cannot work their body correctly
Straightness is a crucial part of the horses development and one of the things they love to evade!
Basically because working with straightness is harder for them then working crooked. But also because it truly is impossible to be perfectly symmetrical.
This is why we get obsessed with dressage. We are forever endlessly seeking the impossible. I say this as lovingly and supportive as possible because I am right there with you relentlessly seeking the impossible!
Now before I manage to completely talk you out of your never ending pursuit of perfection that is dressage, the purpose of the way the exercises and movements are tiered throughout the levels is to address the ways the horse will naturally evade that way of movement.
For example, prelim introduces circles and serpentines that create the looseness and suppleness for the relaxation and swing required for a prelim working paces.
Novice introduces leg yield, lengthening the paces and smaller circles to create the engagement and throughness required for novice working paces.
Elementary introduces shoulder in, traver, rein back and simple changes that create the elevation and collection required for entry level collection.
And so forth up the levels.
So when we are talking about straightness we are talking about maintaining the connection from hind end to contact for the level. We are talking about stacking the horses building blocks on top of each other as evenly and balanced as possible. We are wanting to get our horse to engage its core and be as even and balanced as they can. The more evenly and balanced they work the less concussion and strain it puts on their body.
Straightness comes from becoming centered, balanced and engaging the core. It is comes from moving their weight into each of their 4 legs so they become “ambidextrous” so to speak. Of the horses I have met mostly they are strong and straight to the right and weak but supple to the left. Straightness comes from developing the tone to be equally strong and supple on both sides.
So when a horse evades straightness they will be twisting through the pelvis, dropping the shoulder, weaker one way than the other or more supple one way than the other. Any of these will put strain and concussion on our horses body which will at best slow their progress and at worse do damage to their body. Not engaging their core puts strain on their back, especially when we then sit on their back and creates tension through their back.