My, self imposed, problem is that I lack the common sense to focus on one writing project at a time. Research it, write it, sell it - then move onto the next project.
I don't seem able to do this. I have cemetery project, the South African postcard project, the old newspapers project and the E+E project in my head at the same time and the number of jobs needing to be done seems rather overwhelming.
The good news is the the Biggles Companion - a project I did complete - is selling well. I make about £10 a week profit from Ebay and word-of-mouth sales. Not a fortune but it amuses me no end.