Sims live all over the world which definitely means they live in some breezy places, and if you put the game on high speed and watch trees and bushes, you’ll notice them sway with the wind. The breeze doesn’t show itself much indoors though since sims usually can’t open their windows. These curtains can be hung in archways or open windows and they will gently sway as if being disturbed by the breeze just like trees do. It’s a tiny detail that makes a big difference!

You can see the curtain swaying here.