From The Letters of Vincent van Gogh:
What is drawing? How does one get there? It’s working one’s way through an invisible iron wall that seems to stand between what one feels and what one can do. How can one get through that wall? — since hammering on it doesn’t help at all. In my view, one must undermine the wall and grind through it slowly and patiently. And behold, how can one remain dedicated to such a task without allowing oneself to be lured from it or distracted, unless one reflects and organizes one’s life according to principles? And it’s the same with other things as it is with artistic matters. And the great isn’t something accidental; it must be willed. Whether originally deeds lead to principles in a person or principles lead to deeds is something that seems to me as unanswerable and as little worth answering as the question of which came first, the chicken or the egg.
But I believe it’s a positive thing and of great importance that one should try to develop one’s powers of thought and will.
I’m very curious about what you’ll think of the figures I’m doing at present, when you see them sooner or later. It’s the same with them as with the question of the chicken and the egg: should one make figures for a composition one has done first, or combine the figures made separately so that the composition flows from them? I believe it comes down to the same thing. Just as long as one works. I end with that with which you close your letter — that we have in common a liking for seeing behind the scenes or, in other words, are inclined to analyze things. Now this, I believe, is exactly the quality one must have in order to paint — one must exercise this power when painting or drawing. It may be that there has to be something innate in us, to some extent (but that too you have, and so do I — for that we may have to thank our childhood in Brabant and a background that helped, much more than is usually the case, to teach us to think), but above all, above all, it’s only later that the artistic sense develops and ripens through working. How you might become a very good painter I don’t know, but I certainly believe that it is in you and will come out.