At the point where a fight gets started are you find yourself inside it, you can be in 3 different states of mind: nothingness, perception or alert.
If you’re in an empty state of mind, where you absolutely don’t percieve the agression comming, you can either have a good or bad reaction, which will be given by your training or inner hability to solve the situation. Since you didn’t notice any sign of the attack, you totally depend on your body: as fast as your body can adapt to the situation, as good your reaction will be. Only by training you can polish this reaction and optimize it to an utmost perfection.
A second state would be when you notice an agression coming, your saki advises you right on the moment it’s getting done, so you have a milisecond to react, time your mind can use to create an intuitive response to the outer stimule, defending efficiently from the incoming attack without elaborating an ordenate response (technique) but an intuitive one.
The third state is that where you can predict the incoming attack, with time enough to prepare your mind for it, and elaborate a complete technique to nulify it.
Ironically, while training, you first polish the technique, and by doing so, little by little, your whole being, body and mind, become more accustomed to sense the surroundings, to react at the minimal impulse, and allows you to further develop the first and second situations, where you need to react without the usage of your mind.