Like water off a duck's back

Origin

For centuries, observers of nature marveled at the duck's peculiar ability to emerge from water completely dry and unbothered. The bird's feathers are coated with a natural oil, rendering them remarkably hydrophobic—water simply beads up and slides away, leaving the duck's skin untouched. This everyday sight of water effortlessly shedding from a duck's back became a vivid metaphor in the English language by the early 19th century, symbolizing how criticism, insults, or troubles can fail to penetrate or affect a resilient individual, much like water failing to soak a duck.