Also, this remark is giving away a fairly limited view on art appreciation:
> While you can learn from failures, only sales strengthen the muscle because only they show that someone actually cares about what you are making
This is obviously not the case for art projects that target only a few people, or art practices that do not result in tangible objects. (Although there are some exceptions, such as Marina Abramovich, but those are very limited.)
Great for them, but this is not about all art. It just is impossible to live of most art forms. This type of art fits well with our economy, and therefore makes a living. That fit is more important than all the business advice put on top.
The article does point out exactly this problem, but glosses over the fact that most artists don't want to change to popular art. Only a few can, and most don't want to.