A lawyer can't really tell you what will happen in a novel situation. They can speak with great confidence about legal precedents and where the law is black and white, but once you start walking into the grey areas, where the law isn't clear and there is no precedent, the law isn't a computer program interpreted by machines. There's a whole layer of human judgement in deciding what happens in that case, you don't just overflow onto the stack and get to rewrite the legal code to suit your needs.
So when a lawyer says something like, "Ahh, but the law only talks about 'checking accounts' and 'savings accounts' not 'checking & savings accounts'", at best they are giving you a preview of the argument they will make to a judge or jury at your trial.
Then future lawyers will be able to refer back to the precedents set in your court case with more confidence.