It becomes 'directional' only when we have a new case to decide and go back to the older case in order to explore its similarities and differences with our own case. As in geometry, it takes two points to make a line. It may well depend too on how we want our own case to be decided. Clearly, there is more art than rigorous science to legal reasoning. Yet, the art can be learned and, within limits, rules for its practice can be described.
Good lawyers are good at legal reasoning.
This means that they can find the rule of a case that is 'better' than its alternatives for a given new application. It does not mean that they can explain how they do this. Law students acquire the skill of legal reasoning by reading hundreds of cases. They get better and better at finding the stronger or more defensible holdings for a given case insofar as these are to be a function of the applicable precedents. But they may not get any better at explaining how this is to be done.