Everyone who is a parent is legally responsible for the wellbeing of at least one child. If all dogs have four legs, then Sally's dog must have four legs. All zebras have stripes. The earth revolves around the sun. The early bird gets the worm.
Smoking causes cancer.
All humans must consume liquids to live. Every effect has a cause. All mothers are parents. All triangles have three sides. Every action has an equal and opposite reaction.