Above is a fossil skull of a T-Rex. It is rare to find a complete skeleton of a prehistoric animal and what Paleontologists must do is put an entire animal together using fragments of the animal's skeleton. It is possible to construct an entire animal with a few fragments of the skeleton. We too know and learn with only fragments and building upon those fragments lead to a complete picture. Think about it, do you know another person completely or do you know fragments of that person and slowly build a more complete picture over time as you add more fragments. It is how we form our personal and intimate relationships with another person. It is learned fragment by fragment over time. If we try and learn a subject of interest, it is fragments over time that give us complete knowledge of the subject over time. It is rare we will know a person after the first date or a subject after one class or chapter. "WE LEARN BY FRAGMENTS!"