Causality principle: The principle which cause must always precede effect. More properly, when an event A ("the cause") somehow persuades an event B ("the effect") that takes place later in time, then event B can’t in turn have a persuade on event A. That is, event B must take place at a later time t than event A, and moreover, all frames should agree upon this ordering.
The principle is best exemplified with an illustration. Say that event A comprises a murderer making the verdict to kill his victim, and that event B is the murderer really committing the act. The theory of causality puts forth that the act of murder can’t have a persuade on the murderer's choice to commit it. When the murderer were to someway see himself committing the act and transform his mind, then a murder would have been committed in the prospect without a prior cause (that is, he changed his mind). This symbolizes a causality violation. Both time travel and faster-than-light travel both entail violations of causality that is why most of the physicists think they are not possible, or at least unfeasible in the general logic.