Success in a personal injury claim is all down to proof.
You must prove that the other party was negligent and that this caused your injury. You must also prove the extent of your injuries, the losses they have caused, and the amounts of those losses.
As you are making the claim, it is for you to prove these things in the first place. It is not for the other side to disprove them.
Each case has its own challenges. Having the right solicitors to act for you and to guide you through can make all the difference in the service you receive and the skill with which your case is handled.