it's the result of gripping UP. you get feeling insecure about your balance, so , natirally, you grip with your lower leg, and you pull upward in order to try and pull yourself downward. and you probably also curl your upper body forward.
think of your legs more like a paper clip, maybe. there's even pressure all down your leg , so you are almost down and around the horse, and continuing to the ground (imagine your heels will dig into the ground , like sort of waterskiing on the ground)
the better you get, thje less you grip at all. you get so yuoi are just sort of "dripping" down the sides of your horse. butm, considering that it's normal to grip, think of it more like the sides of scissors pushing down and in on the hrose, rather than the points of pliers pinching inward on two points