One day after school, as he was in this room, he realized that there was a little slit in the shades that light could pass through. The light projected an image of the scene outside onto the ceiling of the room. Cajal also realized that when the opening, or aperture, of the light became larger, the image became less focused, and as the opening became smaller, the images became more focused.

             Cajal thought at the time that he had discovered something new. Later in life however, he realized that this discovery, the camera obscura as it is known, was discovered two centuries earlier by Leonardo Da Vinci. He presented the discovery to his friends who dismissed it as "natural". This is when Cajal first discovered his interest in looking deeper into things. He wonders even as a young boy, how much human knowledge is lost because important discoveries are dismissed as "natural". Cajal's interest in finding out why things work the way that they do is what makes him such a great scientist later in life.

             Cajal's natural interest in exploring nature, and his brilliance, alone are not enough to make him a great scientist. His education was also very important to his development as a man as well as a thinker. His father was essential in Cajal's education. As previously mentioned, the young Cajal often neglected his schoolwork for other activities. He did not take enough responsibility in his own development, so his father had to intervene. At the age of twelve, Cajal was sent to a school in a new town. At first he was bitter about leaving his friends behind, but in the end this move was probably best for him. His education proceeded much more smoothly than before, although he still was not what would be called a model student. When he took the time to devote himself to his studies, he had no trouble achieving high marks on exams. However, when Cajal was uninterested in his studies he continued to make trouble.