And the closer you get to accurately conveying the canon appearance, or to your own skewed mental images, the more accomplished you feel.
Because it's truuuuueeeee! I think fanartists have somewhat a bit of technical freedom in that aspect because we can either make fanart super photorealistic or comepletely stylized; but as long as it's recognizable to the fandom, one is just as good as the other. I love that sort of artistic flexibility!