What is egg-shell skull rule in English tort law?

The egg-shell skull rule is a principle in English tort law that states that a defendant must take a plaintiff as they find them, meaning that the defendant must accept the plaintiff as they are, even if the plaintiff is more vulnerable or has a pre-existing condition that makes them more susceptible to injury. The defendant is liable for all of the consequences of their actions, even if the plaintiff's injury is more severe than would normally be expected.