Representing 1x1 RPers, I'd say the failures I've run into are with consistency, especially if the RP lasts for a long time. I've been super disorganized for years and often forget key details in the plot or about my characters, so I spend way too much time going back through pages and pages of posts to find what I wrote like a year ago (thank you, control F) whenever it becomes relevant again in newer scenes... Or sometimes I just don't bother, and my partner reminds me that the post I just wrote contradicts something important, and I have to rewrite it xD I'm getting better at it now that I've started taking notes, but it's still a struggle because I don't keep up with them very well.