The article talks about people who weren't simply artists but were "greats". I think one thing that causes someone like that to be so questioning is that they lack a good basis of comparison -- especially pre-internet era. These days, I think it is easier to connect to those rare few individuals "like" you in some way if you are at odds with most of the folks around you IRL. But, even so, if you are doing something way out front, to whom do you realistically compare yourself and to what do you realistically compare your work?