Stress
Some people don't deal with stress all that well. Michelangelo was one of them. He did not like to bathe very often, even by fifteenth-century Italian standards. Once he removed his shoes and had much of the skin on his feet come off. Mmm…appetizing.
Van Gogh is obviously the poster child for poor stress management. Why was he so stressed out? For one, he only sold one painting in his lifetime. Secondly, Van Gogh had somewhat of a stressful relationship with Gauguin. In the heat of an argument with Gauguin, he cut his ear off. He then gave his ear to a prostitute. Needless to say, he was soon hospitalized. During his life, Van Gogh created many works such as Irises and Starry Night. Unfortunately, he ended his life in 1890. With one ear still intact.
Being a painter is stressful. Your work may not be well received or galleries may decide not to show your work. When you don't finish a painting or it's not well received, you may feel despair and agony. It can feel like a major rejection.
Because being an artist is so stressful, it's important to create work that you truly believe in. For instance, if Marcel Duchamp had listened to his critics, he may never have created Nude Descending a Staircase No. 2. When Duchamp submitted the painting at the Cubist Salon Des Independants, the jurist asked him to paint over the title. Duchamp refused and decided never to be part of a group again.
Sometimes, you'll feel like you're all alone in the world. But it all comes with being a painter.