When that happens, I tell myself I can do one of two things... quit and do engineering or give myself a challenge. If this happens to you I suggest you take the challenge (the other choice is too horrible to talk about in an art blog)
My challenge to myself? Back lighting and bright sunshine. I know, I know...you think I'm going crazy. Not to mention the star of the painting is in motion....walking towards the viewer (one of my personal, all time, freeze up and run away subjects in painting)
Not only that but then I throw in a busy background.... I need a stiff drink?.....Ice tea please.