When the enemy aircraft comes into radar contact, more information about the speed, size, maneuverability, etc. of the aircraft becomes available. Unfolding circumstances become much more important and it becomes imperative to make a first decision based on known information. The pilot is observing the actions of the enemy aircraft and is orienting and analyzing the data. All this leads to the pilot taking an action and then reacting to the unfolding interaction with environment. When the dogfight begins, there is little time to devote to orienting unless some new information pertaining to the actual identity of the attacker comes into play. At this point, the information is cascading in real time, and the pilot does not have time to process it consciously, he just acts according to his training.
If the opponent is any good, he is going through the same cycle. The trick for our pilot is to interfere with the opponent's OODA cycle. This means the pilot must change his speed, direction, altitude, etc. quicker than the opponent can change his. The pilot must think and act quicker than the opponent can think and act. This is one meaning of the phrase "getting inside the opponent's OODA cycle." The other meaning derives from the military strategies first developed in Sun Tzu's Art of War. It involves getting inside the opponent’s cycle and thinking processes by creating opportunities for the opponent to see react to an action as though it were something else, causing him to react inappropriately. A key is to obscure your intentions and make them unpredictable to your opponent while you simultaneously clarify his intentions. Act quicker to change circumstances faster than your opponent may adapt or react to. Create confusion and disorder to cause opponent to over or under-react to situations that appear to uncertain, ambiguous, or incomprehensible.
In a self-defense situation, this mean you must be alert and observe everything happening around you, orientate and analyze this data, make a decision based upon the data, and take an appropriate action. You must complete this cycle quickly; quicker than your opponent can compete it during combat, more slowly in other times, but you must always follow the loop.