Why do sterols work as rigidity buffers in the cell membrane

Why do sterols work as rigidity buffers in the cell membrane?

Sterols are essential in all eukaryotic cell membranes. Sterols reduce membrane fluidity and permeability, and increase membrane rigidity and strength. Together with sphingolipids they help organize regions of the membrane into lipid rafts, microdomains in the plasma membrane with increased rigidity, that organize cell signaling proteins into functional complexes.