The answer is both yes and no.
Everything that’s considered “instinct” by most people are actually based on experience or confused with reflex. What most fictional worlds mean by instinct is the character did it without thinking about it and serves as an easy justification for why the character could behave as the plot demands. The problem with this method of thinking is that it drives directly against what instincts are.
Instinct is your Fight or Flight response.
99% of the time when someone’s referring to instinct, they’re usually talking either about their reflexes or about a learned behavior. Your responses to different situations can be trained and are constantly being updated as you gather new information.
Combat training will retrain your “natural” responses to situations and stimuli. A character isn’t going to load and fire a pistol off the cuff, pull off a proper punch with no outside stimuli, or notice when a fight’s about to start if they have no understanding of human behavior. You can be trained, passively by life experience, aided by outside stimuli, or intentionally, to perform or recognize these actions. You can become so practiced at them that they become reflexive and you do them without thinking about it. That’s the point of training and practice, to teach you how to act without being slowed down by your thoughts.
Now, any behavior you practice or pattern you follow can be exploited by someone who knows it’s there.
Say you get into a practiced pattern where you always show up at home five minutes after five at the end of the day. If someone was unsure where to find you but knew you’d always be home at exactly five minutes after five, then they could move to intercept you.
Combat does this all the time. A technique becomes a practiced pattern of behavior, one that has moved from thinking to automatic. However, the more a technique is in use then the more others become aware of it and how it works, they develop their counters to it.
Feints in martial arts are about disrupting what as become your instinctual reaction to an incoming blow, in order to trick you into reacting to a false action so that your defenses are opened and your opponent can hit you.
A common beginners combo in Taekwondo is the backfist and right punch.
The martial artist throws the backfist as a feint, the backfist catches in their target’s peripheral vision and they raise their front hand to block. The martial artists switches to punch them in their now open midsection.
The basic thought is: if I flash my hand in your peripheral vision, your first instinct will be to raise your hand to stop it. Sometimes, you’ll raise both hands. Sometimes, you’ll even turn your head to protect from harm. Best case on top of everything else is you closing your eyes in preparation for the hit.
When this happens, I have opened up your whole body to do whatever I want with it.
Your body’s natural instincts will always protect what your body prioritizes as its most important parts. These are the parts it needs to keep existing. These are your head and your internal organs. This is why when you’re injured, your body always moves to curl up into a ball. When you’re trapped on the ground, your first instinct will be to roll over.
Protect the head. Protect the center.
It is more complicated than this, but on a simple level this is what the natural human reaction to injury is.
Combat exploits those reactions, even the most basic cheap street fight techniques.
Here’s the rhythm:
1) You get sucker punched in the gut.
Natural reaction: You bowl over. Your head and arms come forward. One by the force of air leaving your lungs, two to protect your stomach, the part of you that was just hit. Your body’s natural reaction is to move the damaged body part away from danger.
3) They grab your head as it comes forward.
Natural reaction: When your body reacts to an injury, it is not normally conscious of its surroundings. The grabbing of the head is the exploiting of this response.
4) They knee you in the face.
Natural reaction: This move is easy enough to pull off that most people have learned it from watching kickboxing, MMA/UFC, or some other type of action movie. A knee strike doesn’t take the same amount of training as a kick. This isn’t a natural reaction at all. It’s a learned behavior.
The general rule of thumb regarding instincts in the martial field is don’t trust them. Use your head instead. Instincts react directly to generalities, they don’t take the situation into account. Your fight or flight could send you running right into a wall. It could send you running at the enemy behind you that you didn’t see. It can be used against you.