Up until this point, we've largely explored matters relating to solid, three dimensional forms. Things with volume to them that occupy space and relate to one another in that space. This last point is something we'll focus on a great deal in the next section.
Texture - that is, what people tend to think of as detail - isn't actually all that different. While we treat it a little differently, texture is also made up of three dimensional forms. The only difference is that these forms adhere to the surface of some other object - and this difference fundamentally changes how we approach drawing it.
An example I like to use is fish. If you've got a fish swimming in the ocean, then we draw it similarly to how we draw the boxes and sausage forms we've tackled thus far. We apply constructional means - drawing through our forms, defining their silhouettes with outlines, describing how their surfaces move through space with contour lines, etc.
If, however, you take a bunch of fish and use it to wallpaper your bedroom, it becomes a texture - and the way we draw it changes. The fish is now a part of the wall itself. If the wall turns, the fish will follow. If you were to strip down this fishy wallpaper and wrap it around a box instead, the fish would come along with it. They cease to be an independent object, but rather become a part of this texture that can be applied to any other surface.
Now, before we get into why that matters, first we have to take a bit of a detour.