Writing on walls

I am writing my sixth contracted book and realise that publication of the others was a mistake on the part of the publishers.
My preferred length is as short as possible; the three sentence story being long enough to say most things.
I love you. Marry me. Let's have children.
Which is how, somewhere in that marathon of writing a book, I hit the wall.
I used to think the wall was an affectation of runners who chase shadows to trump their personal best.
I am not a runner, preferring the sure determination of the long distance walker over the histrionics of road eaters.
I do have the wall of endurance in common with marathon runners, that point when sanity says give it up, have a smoke and a cup of tea, in a china cup.
But, so far I have written through it and submitted the manuscripts on time and the publishers were too busy to notice that it was the work of a chancer bent on admiration and a royalty cheque.
Then readers say they like the stuff. Try as I might I can never re-find that wall that bothered me so much that I took the dog for a walk instead of writing any more.
Maybe I'll take up painting and see if that's any easier, after I deliver this book, and the one after that which is also contracted by another foolish publisher.
I can write anywhere, mostly in my head, and painting requires you be somewhere, which is a bit too much bother.
Storytelling here