a plan & an idea

A question : "what makes somebody starting drawing?". Is it because there is a slide, a dia-positive of an image, in the head? And the drawer projects it with an inner light through the lenses of the eyes on paper? So the hand can follow the projected lines, the contours of the enclosed area's, to remain the necessary white reservoirs of clean paper? Is drawing giving birth to an idea or is it executing a plan? Both, it isn't or - or, it's and - and.
The first drawing ever could it have been a single line drawn with charcoal? Or was it the print of a hand covered with mud? Or the negative of that hand by using a spray of mud over the hand on a stone surface. So, was it a single line of charcoal, the print of a hand, the left over of a hand? Or could the first drawing been made by five fingertips dipped in mud to draw five short lines...
I suppose there wasn't any idea or plan. The acting person didn't foresee what she was doing, perhaps she was surprised. As in Stanley Kubrick's film "2001 a space odyssey" monkey's where surprised while playing to discover a bone could be a weapon to hit with (civilisation was born). So, being surprised and amazed by making traces by hand. From than drawing is going to develop fast, draughtsmen discover and develop to draw after imitation of reality by drawing animals. Drawing is mimesis, imitation, a scheme, a depict or treat in a mannered and non realistic style.
The question was the difference between plan & idea, in order to start drawing.
PLAN : an intention or decision about what one is going to do.
IDEA : a concept, mental impression, opinion, a belief or a feeling that something is probable or possible.
The surface research project which is trying to work systematically on palimpsest drawings started not as an idea but started as a plan to execute. Perhaps a little, small idea is in it, some content that can be interpret. But that content is a glimpse of something, an encounter like a flash. It's tiny -, very tiny, content.