You curtsey to show respect to someone; holding your ground shows self-respect.
"A curtsey is in grace what an adagio is in music." — Graham's magazineSpecifically, from The Lady's Book:
Bend your arms gracefully, lightly holding out your dress.
Bring the front foot into 2nd position.
Draw the back foot into 3rd position behind and then immediately into 4th.
With the weight on the front foot, bend the front knee and gently sink.
Shift the weight to the back foot and rise.
Return the front foot to 4th position.
Here is a video demonstrating an early 19th century curtsy, but, as you can see, it's quite a bit different from the curtsy explained above.
I recall the actresses in an Austen movie being taught to melt into a curtsy.
"The perfect curtsey is rarely performed in society."I can see that! The search for the perfect curtsey goes on...