Truth. Or, rather, the lack of it. Narrative building matters so much, hence:
When the facts are on your side, pound the facts.
When the law is on your side, pound the law.
When neither is on your side, pound the table.
I've spent a lot o' time in a courtroom and seen the arguments that go into such things as wording of jury instruction for this exact reason. The law is a component, but far from the only one. Civil law is even worse than criminal in this regard, IMO.
Respectfully, I can see you've not spent much time in a civil court. The standards of evidence and burden of proof are rather lax compared to a criminal trial. See above. In very broad strokes, civil trials are not "beyond a reasonable doubt", but rather "by the preponderance of the evidence". In every day terms, your goal is simply to show it's more likely than not that the other party caused you the harm/loss.