It is often difficult to determine which, if either, of these concepts apply to later lawsuits that are seemingly related, because many causes of action can apply to the same factual situation and "vice versa". The scope of an earlier judgment is probably the most difficult question that judges must resolve in applying "res judicata". Sometimes merely part of the action will be affected. For example, a single claim may be struck from a complaint, or a single factual issue may be removed from reconsideration in the new trial.