You don't. That being said, it's important to realize this only applies to civil cases, which are decided on the balance of evidence, not "beyond a reasonable

You don't. That being said, it's important to realize this only applies to civil cases, which are decided on the balance of evidence, not "beyond a reasonable doubt". Absent any other factors, it's more likely the the car caused the accident. This is just like the default assumption that, absent any other evidence, if there is a rear-end collision, the fault lies with the person in the rear, even if the person in the rear claims that the person in front actually threw their car into reverse and was driving the wrong way.