"Do as little as possible, to do as much as possible"
Was what a visiting clinician told me once, when I was really struggling to get shoulder in on a young horse. I was trying to do far too much. He got me to just take a deep breath in, let it out slowly, make myself go floppy and just put my body in the position to ask for shoulder in, while letting everything just hang and relax. And what do you know, shoulder in, dead straight, so soft, straight down the long side.
I think we get so caught up in correctness, trying to make everything perfect, that often we forget to breathe, or allow tension to sneak into our bodies while we ride without noticing.