In common-law legal systems, the guiding principle is the doctrine of stare decisis. This principle means that courts should follow precedents set by previous decisions when deciding cases with similar facts. The idea behind this principle is to ensure consistency and predictability in the law, so that individuals and entities can have a clear understanding of legal outcomes based on past decisions.

Let's break down the concept further:

1. Consistency: By adhering to previous rulings, courts maintain a consistent application of the law. This consistency helps to ensure that similar cases are treated similarly, which is a fundamental aspect of fairness in the legal system.
2. Predictability: When the law is applied consistently, individuals and businesses can predict the likely outcome of legal disputes. This predictability allows them to make informed decisions and plan their actions accordingly.
3. Stability: The use of precedent contributes to the stability of the legal system. It prevents frequent changes in the law, which could lead to confusion and uncertainty.
4. Efficiency: Relying on established precedents can make the judicial process more efficient. Courts can resolve cases more quickly by applying existing legal principles rather than re-evaluating issues from scratch.

In summary, the principle of stare decisis serves as a cornerstone of common-law systems, promoting a legal environment where rules are applied uniformly, and outcomes are foreseeable. This principle is essential for maintaining the rule of law and ensuring justice is administered fairly and reliably.