Arguably, when someone can not concentrate is because you have a fear diffuse. We can concentrate when we attack.
Looking at nature we see that animals have adequate anatomy where they live and their natural temperament.
Thus, animals that have eyes in the frontal plane, (cats, apes, owls) are hunters and those who have eyes in the lateral plane, (horses, cows, chickens), need to take care not to be devoured.
In other words, hunters may converge their eyes to attack prey that will give them food, while the hunted can see all around without moving his head.
Hunters just look forward and the hunted look all around.
This will lead us to suppose that animals can focus his eyes, (make it converge on a point on the front), are aggressive, while animals that can see around are elusive.
With these data we observe nature what happens to humans.
Given the location front of our eyes are predatory animals. When we are threatened, or we stand with his back to a wall or we partner with other human beings so that, together, we can see around us.
Aggressive animals like us pay attention to what is ahead and we can not attend the rest of the stage, though, when we are afraid of what surrounds us, we stop paying attention focused and try to pay attention to the environment.
Looking only later in predatory attitude is stay focused and pay attention to everything a little, is to be decentralized, perhaps distracted.
When someone is concentrated in aggressive, combative, attack and when someone is decentralized is defensive, frightened.
Aggressiveness and fear we focus distracts us.
Note: Original in Spanish (without translation by Google): El temor y la falta de concentración.
(Este es el Artículo Nº 2.081)