Do mistakes exist in art?

You've probably heard the saying "there are no mistakes in art" popularized by many authors and painters, including Pablo Picasso. 

Hearing this phrase during a challenging art workshop might come as a soothing comment from your art instructor, but is it a valid commentary?

Let's suppose it is true. If there are no mistakes in art, how do we judge quality of outcome? Surely in other arts, such as music, mistakes exist, and we know it immediately when that wrong note is played during a performance.

But in painting, if mistakes don't exist, and anything goes, then failures can never happen. This means that quality of the art has nothing to do with the execution, skill and efforts of the artist, and the distinction between good and bad art is null. In other words, standards do not exist if there is no measure of quality in art.

But standards exist in all the other arts, so why not the visual arts?

Perhaps this is a symptom of modernism which, more than a hundred years ago, discarded all the rules of art, including aesthetics, quality, craftsmanship.

Or on the other hand, maybe this is a by-product of coddling student artist, in the sense of "everyone gets a trophy."

I've made mistakes

I can testify that mistakes exist, as evidenced each time my painting goes in the opposite direction as intended. When trying to paint or draw a portrait, and the mouth doesn't look right, then its a mistake. 

Why do teachers say this?

Perhaps denying mistakes is an effort to protect the student so that they don't feel discouraged. But is mistake denial really helping the student?  Does it really help a person to claim that they are infallible when it comes to art? The answer might be found in the scenario where everyone gets a trophy, which has been proven to actually cripple a student preparing for the future.

What if it's true that there are no mistakes in art?

If there are no mistakes in art, then quality doesn't matter, and there would be no benefit to improving one's skills. Why put the effort in if it doesn't matter anyway?

Quality matters in all other aspects of creative arts, such as music, and theater, so why not art?

Some people attempt to lay it at the feet of the artist's intent. But surely the artist must have intended something. Whether the artists realized he or her intentions or not would be how I would measure errors. If they did what they set out to accomplish, it's not an error.

Conclusion:

I reject the claim that there are no mistakes in art, because art, by definition, is intentional. Intent cannot be satisfied in the face of unintentional results. Plus I frequently make mistakes in my paintings, so mistakes do exist.