A more thorough explanation:

The doctrine of contra non valentem is a legal rule that states that a limitations or prescriptive period does not begin to run against a plaintiff who is unable to act. This is usually because of the defendant's culpable act, such as concealing material information that would give rise to the plaintiff's claim.

For example, if a doctor fails to inform a patient of a medical condition that the patient could not have reasonably known about, the patient may not be able to bring a claim against the doctor until they become aware of the condition. In this case, the doctrine of contra non valentem would apply, and the limitations period would not begin to run until the patient becomes aware of the condition.

Another example could be a case where a person is injured in a car accident and is unable to bring a claim against the other driver because they are in a coma. In this case, the doctrine of contra non valentem would apply, and the limitations period would not begin to run until the injured person is able to act.