In computer programming, there is a kind of programming called modular programming. In this technique, a giant program is broken up into independent smaller units. Each unit in itself a complete program to achieve a sub goal. These units are called “Modules”. All these modules are archived in the libraries like math and header libraries in C++. These modules can be used in any other program where they can accomplish the same task.
These modules are very handy and only additional programming lines are added to expand their capabilities. For example, suppose you want to write a program to draw a colored circle and we already have a module to draw a black lined circle, only additional code required to be written is the coloring code. This saves the time and money. This technique is called reusability of code. The integrated code again is archived and becomes available to reuse in future. The library gradually builds up.
I think human brain also works this way to become efficient and draw only those inputs as are absolutely necessary. As we grow older, library of event builds up and less and less inputs are required to conceive a situation at hand. Brain does not want to cram its limited space with copies of events which have some portions common to each other. Only newer details are added.
Brain receives inputs through sensory organs like eyes, ears, touch, smell etc. Eyes are visual organs and have receptors which are made up of cones and rods. But most of the cones are concentrated in the 10% area around the center. This is the reason we have to move our eyes to bring he object of interest into the focus of center. Eyes scan too much information but the brain does not use it in the entirety. Suppose, we see a dog, the brain which have already has a picture of general features of dog in its library only seeks the newer traits like color, size and what the dog is about to do.