While it's true that courts can sometimes make what sometimes seems "surprising" rulings I don't think that's a reason to be timid. Of ten times those "surprise" ruling are made in lower courts that get overturned. Even for higher courts the "surprise" rulings can be targeted toward a very specific set of circumstances that don't otherwise affect the law as a whole.
One of the reasons laws are published is so citizens can read them and know what the law is. Courts go by the written law and rely on precedent. One reason lawyers refer to previous rulings is because it can show a mindset that there was reliance on previous understanding of what the law was when an action was taken.