A more thorough explanation:

The aggravation rule is a principle in workers' compensation that states that if an on-the-job injury combines with a pre-existing injury, resulting in a greater disability than what would have resulted from the on-the-job injury alone, the entire disability is compensable as if it had occurred at work.

Let's say an employee has a pre-existing back injury from a car accident. While at work, they lift a heavy box and injure their back again. The aggravation rule would apply if the employee's disability is greater than what it would have been if they had only injured their back at work. In this case, the entire disability would be compensable as if it had occurred at work.

Another example could be an employee with a pre-existing knee injury who slips and falls at work, aggravating the injury. If the resulting disability is greater than what it would have been if the employee had only injured their knee at work, the aggravation rule would apply.

These examples illustrate how the aggravation rule works in practice. It ensures that employees are compensated for the full extent of their injuries, even if they had a pre-existing condition that was aggravated by a work-related injury.