Mitigation of damages is a rule in California, that says if you are injured because of someone else's actions, you must do what you reasonably can to recover from these injuries. In essence, reducing or minimizing the harm you suffer due to the accident.
For example, someone injures your leg. You can go treat it with the doctor and fully heal, but instead you let the injury get worse until a major procedure needs to be performed on your leg.
If the defendant can prove that you would have suffered less if you took reasonable steps, then the jury can reduce your award. However, the mitigation must be reasonable according to the specific facts and circumstances. There must not be undue hardship and difficulty in the steps you take to mitigate damages.
This rule is designed to eliminate an intentional run-up in costs by the plaintiff, trying to recover more money.
Even though you did nothing wrong, and the accident was someone else's fault, you still have a duty and responsibility to take care yourself and limit the extent of the harm caused by as much as possible. A plaintiff should not be compensated for harm that could have been avoided by reasonable effort and actions.
The law only requires you to take reasonable actions, not the correct ones. So if you are faced with two options to mitigate damages (i.e. receive medical treatment) and one is technically better than the other, you will no be punished for choosing the other one. You must only act diligently, reasonably, and in good faith.
The duty to mitigate is not a bar to recovery. In other words, if it is determined that you did fail to mitigate damages, it does not prevent you from recovering anything. It just reduces your recovery by the amount you could have avoided.
This rule applies in two major areas with car accident cases. There is a duty to seek reasonable treatment to recover from your injuries. So if you sought reasonable medical treatment soon after the accident, and continued to treat regularly with the doctors involved, you will be deemed to have mitigated damages.
The rule also applies when you make a claim for lost wages. If you are cleared to go back to work, but you refuse to, this may reduce the amount of lost earnings you claim.
So it's always good to coordinate with your attorneys and doctors in order to minimize this argument by the defendant.