In some personal injury cases, the defendant may make the argument that the injured person is actually to blame (at least partially) for causing the underlying accident.
If you do share some level of liability, it can end up affecting the total amount of compensation you'll end up receiving from other at-fault persons and businesses.
In shared fault injury cases, California follows a "pure comparative negligence" rule. In basic terms, the amount of compensation you're entitled to receive will be reduced by an amount that is equal to your percentage of fault for the accident.
As an example, if in a car accident where the other driver blatantly ran a stop sign, but you were driving a few miles an hour above the posted speed limit at the time, you might share 10 percent of the blame for the accident, while the other driver is 90 percent at fault. If your losses (damages) add up to $10,000, how does your shared fault for the accident impact your compensation? Under California's pure comparative negligence rule, your compensation will be reduced to $9,000 (or the $10,000 total minus the $1,000 that represents your share of fault for the accident.)
While courts in California are obligated to follow this rule in an injury lawsuit that goes to trial, it may be a different story if you're dealing with an insurance adjuster outside of the court system. An insurance adjuster may raise the issue of California's comparative negligence rule during settlement talks, but you're free to negotiate what the impact of that rule should be on your claim.