When you look at a person, what you perceive is not a series of shapes and colors that correspond to what's there, but rather a bunch of hastily constructed symbols that convey the information that the brain thinks is important. If you haven't rewired your brain for drawing, then "important" questions do not include "Is that elbow angled at 90 degrees or 75?" or "Where are the eyes in relation to the top of the head?" Instead, what you usually care about are things like "is this person happy, or angry?" and the information that gets recorded is a little tag that says "Smiling" with a vague curving-upwards-line symbol accompanying it.

I suppose you could say that ordinarily when people attempt to draw things they instead do something more like diagramming them?