When mentally preparing for a defensive encounter, ensure that you are taking into account your ability to reason and make decisions under stress. The best way to ensure that this happens is to make these decisions before you get to that encounter.
OODA and Preparing for the Fight:
Some may have heard about Colonel Boyd's OODA loop. In a nutshell, a person OBSERVES a stimulus, they ORIENT themselves to that stimulus, then they DECIDE a course of action, and finally they ACT, carrying out that course of action.
The Boyd's idea is objectively true and sound and has spawned a series of related theories. Some use this as a basis to work your plan to disrupt your attackers OODA loop. To the point, if you make the person react to you, you can keep them reacting to you rather than taking the offensive and making you react. Some say that thinking faster is necessary and knowing the OODA loop helps that while others say that we cannot accelerate the OODA loop and it is more important to act sooner rather than faster.
Boyd's point of the was more about having a planned response to a give stimulus. This allows for the brain to skip over the DECIDE step and move right into the ACT. If you have a simple plan ahead of time, you can execute it based on the actions of the attacker, without having to decide what the course of action SHOULD BE in the moment.
"Everybody has a plan until they get punched in the mouth" Mike Tyson
If we don't have to think about our plan, just execute it, the problem becomes much more simple.