What is the “thin skull” rule that makes a plaintiff liable for injuries caused to her by the tortfeasor?

The ‘thin skull’ rule makes the tortfeasor liable for injuries caused to the plaintiff even if those injuries are unexpectedly severe due to a pre-existing vulnerability or condition. As indicated in Athey v. Leonati at parag. [34] ‘The tortfeasor must take his victim or her victim as the tortfeasor finds the victim, and is therefore liable even though the plaintiff’s losses are more dramatic than they would be for the average person.’