A more thorough explanation:

The just-as-probable rule is a doctrine used in workers' compensation cases. It states that if an injury is equally likely to have been caused by a non-work-related event as it is by a work-related event, then the workers' compensation claim will be denied.

Let's say an employee claims that they injured their back while lifting a heavy box at work. However, the employer argues that the employee's back pain could have been caused by a pre-existing condition or by lifting something heavy outside of work. If it is just as probable that the back pain was caused by a non-work-related event, then the workers' compensation claim may be denied.

Another example could be an employee who claims they developed carpal tunnel syndrome from typing at work. However, the employer argues that the employee also spends a lot of time typing outside of work, such as for personal projects or hobbies. If it is just as probable that the carpal tunnel syndrome was caused by non-work-related typing, then the workers' compensation claim may be denied.

These examples illustrate how the just-as-probable rule is used to determine whether an injury or illness is truly work-related and eligible for workers' compensation benefits.