The year I learned to write C code I was 19, second year of university and already willing to drop out, so I started spending time with C and 3D graphics. I was just fresh of the math exam so the 3D matrix transformations to do rotations was trivial to implement. I just wrote a function to draw triangles, used a simple z-sorting technique, and the basic shading calculating the cosine of the angle between the observer and the surface. With just these basic things I ended up with 3D "worlds" similar to the ones I saw in DOS games when I was a child. All the effort was maybe 500 or 1000 lines of code, but to build things from scratch, only starting from the ability to draw an RGB pixel, gave me a sense of accomplishment that later shaped everything else I did. I basically continued for the next 20 years to create things from scratch.