first year student with an issue

Because it's not as black and white as that.

For a start, consider that each case will have its own set of facts and evidence. The legal team representing the parties need to present their evidence in the most persuasive manner possible (and make sure it is admissible). It's often the case that the connection between the facts and existing caselaw is not exact - if it was, odds are the matter would have settled a long time before it got to court.

Second, there is the burden of proof and standard of proof. Which party must prove their case? And must they prove 'beyond a reasonable doubt' (ie criminal cases) or 'on the balance of probabilities (ie civil cases)?

Then there is our court system generally. We have, in most instances, an adversarial system where both parties are required to lead evidence and progress their argument. This is opposed to an inquisitorial system where the 'judge' has the primary responsibility to seek the information.

Lastly, in a proportion of instances (I couldn't say how many), judges will pull the information for their judgments directly from the arguments and submissions of the parties - usually the successful ones.