A person who has been injured in an accident and brings a lawsuit to obtain damages always has the onus of proof to prove their claim. The onus of proof in a civil claim is quite different from that in a criminal matter. In a criminal case the evidence must establish guilt “beyond all reasonable doubt”. That is a very high standard of proof.
In civil claims the onus is “on a balance of probabilities”. This is a significantly lower level of proof required. A balance of probability essentially means that “something is more likely than not”. It is sometimes described as being 51%.
You may have seen photographs or statues where someone is holding the scales of justice. In those images you will note that the scales are tilted slightly to one side or the other. If the scale is tilted to one side then that is the balance of probability.