Sometimes an accident happens which is not entirely the fault of one person. Sometimes the fault is shared.
Most often in this situation it's predominately one person's fault, but the other person is at least partly to blame for their own injuries. In this situation the person concerned is still entitled to compensation, but they just get slightly less of it.
Let us say for example that you are injured in an accident which is 80% the other person's fault, but 20% your own fault. In that situation the correct way to go is to work out what compensation you would be entitled to if it was 100% the other person's fault, and then knock off 20% to reflect your fault. So you still get compensation, even if not the full amount. So it's still worth claiming even if you think that the accident was partly your fault.