For the artist drawing is discovery.
And that is not just a slick phrase, it is quite literally true.
It is the actual art of drawing that forces the artist to look at the object in front of him, to dissect it in his mind’s eye and put it together again; or, if he is drawing from memory, that forces him to dredge his own mind, to discover the content of his own store of past observations.
It is a platitude in the teaching of drawing that the heart of the matter lies in the specific process of looking. A line, an area of tone, is not really important because it records what you have seen, but because of what it will lead you on to see.
Another way of putting it would be to say that each mark you make on the paper is a stepping-stone from which you proceed to the next, until you have crossed your subject as though it were a river, have put it behind you.
John Berger: Berger on Drawing. Aghabullogue, Co. Cork: Occasional Press (II edition, 2007), p.3.