Awareness of the outside world. Phys.org: Why do cats lick and chew catnip? Researchers find an answer. Press, June 14, 2022.
Situation. You are in the ring with other riders. Everyone is doing their own thing. You & your horse are chilling at the walk.
I was always taught that you yield the rail to those who are working. You stay OFF the rail to stay out of the way.
In a saddle seat ring, you never pass between another rider and the rail. Therefore you stay ON the rail to stay out of the way, so that folks can pass you on the inside.
You can see how this would lead to a certain amount of confusion for those of us switching between disciplines.