Art education is a part of the requirement of becoming a good artist. It is true that not all attend a formal training, some are self-taught, but all are educated to some degree, even if only through practice.
Small children begin drawing and perfecting their skills as they grow. We usually see round heads with hair coming out from the top and stick bodies with stick limbs in the beginning. Most children begin by drawing their family, house and family pets. Later they experiment with other items.
Some lose interest and others continue pursuing the field. With practice their skill flourishes. As they continue to draw they not only get more accurate with the depictions but they also get quicker at the drawing itself.
The key is that an artist must learn to memorize what things look like. They must truly understand the human anatomy and how it moves. Not only basic human anatomy but the differences in the human body as it ages.
The many fabrics can pose a challenge to the artist as well. A leather blanket would certainly drape differently than one made of cotton. Lighting is the essential ingredient that can make a drawing come to life. All artists must study lighting and learn that it travels in a straight line but it reflects off some objects and is absorbed by others.
Consider the changes in the skin from infancy to old age. That must be shown in art. The same is true when the model is a young tree as opposed to that of a tree that is 50 years old. The bark would be very different indeed!
So you see, every artist is trained to some degree, whether he attends a class or not he must be taught. There are many good books on the subjects of art and drawing that can assist with the mechanics of drawing but only the artist can provide the essential element. That is the key ingredient without which the finished product will never be considered art.
I am referring to the mindset of an artist. Just as I mentioned, an artist takes into account even the smallest detail of his surroundings and notes it to memory, for he never knows when it may come into use.