Because he is famous for some "wild" art and for his mental breakdowns late in life, many are not aware of the precise and powerful mind that Vincent van Gogh had, but his letters are ample testimony to that.
He was not just an intuitive artist, he applied a lot of knowledge and thought to art, both his own and others'. For example this was the first letter I happened to look up on that site.
"Speaking of Van der Weele, I remember saying to him about the picture which he got a medal for in Amsterdam - and this contrary to the opinion of others - that I greatly appreciated his having succeeded so well in preserving the unity of STYLE despite all the different things that appeared in it, and that it really and truly was a picture, i.e. something quite different from a realistic study from nature."
I suspect Vincent was amongst the pioneers of those appreciating the importance of seeing art as being something else than skillful copying of the world.