1. Van Gogh's weakness is shown through his portrayal of himself with a bandaged ear. he seems to be highlighting his unstable mentality at that time, such taht he even cut off his own ear, which is his weakness.
Van Gogh could have shown his weakness freely in his self portrait, unlike other artists, perhaps because he want to be different from the norm. Even as a post-impressionist, his style was considered unconventional and unique, thus, he could have desired to deviate from the norm, thus portraying himself in a undesirable light.
He could also have been suffering from depression during that time, as we know that this self portrait was painted during the last few years of his life, and during that time, he could have been feeling depressed about his life, which led to him eventually commiting suicide. He could have shown himself with his weaknesses for all to see as he has a low self-esteem, brought about by his failure in his career so far, only having sold one painting in his life, thus, he could have felt that the only things worth remembering about his life is all the unfortunate and sad things that have happened to him, thus, he portrays himself not as a joyful person, but in a sombre and sad way.
By portraying himself with his weaknesses, Van Gogh also showed what his emotions at that time was. So, He could have done his self-portrait in this way as a form of expression of his negative feelings.
2. The mood of this artwork is subdued and depressed. This mood is given off by the use of dull colours. These colours used are mostly monochromatic, in various shades of green. These shades of green, even the yellowish-green of the background, all seem dull and washed out, thus adding to the feeling of the artwork being subdued by making the artwork seem rather dull. The facial expression of the artist is also a serious one, further adding to the subdued mood of the artwork.
The excessive use of green, a cool colour, provides a rather depressing air to the artwork, and also, due to the dark green and blacks used on the artist's clothes and hat, the viewer is inclined to think that the artist's feelings are quite negative, further adding to the sombre mood.
I know that this artwork was painted during the last few years of Van Gogh's life, and shortly before this was painted, the artist had gotten into an arguement with his good friend, Gauguin, after which he cut off his own ear. This artwork, therefore, when put into that context, can be seen as an expression of the artist's sadness of having fallen out with his good friend and his depressed and unstable mentality, which could have been slowly worsening until a year after this work was completed, when Van Gogh commited suicide. Thus, upon knowing the events surrounding this painting, the viewer would naturally understand and feel more strongly Van Gogh's depression.