I had previously broken through the "I can't write at all" barrier by keeping this blog (which, for the first seven years I wrote daily, also in bed with that first cup of tea at my side). Some days I struggled with my books because the impostor syndrome would descend. The committee inside my head would give me a withering look, and then one of them would say sternly, "Who are you to think you can write a book?".
The committee inside my head needed to be put in its proper place. "Pretend you are just writing a blog post," I would say to myself. "You can write a decent blog post in half an hour. Just do that."
And that got me started each time, to the point where I had a sort of draft that was worth working on, or some paragraphs that were worth saving. There was always some nonsense that was only fit for the bin, and there was often a page or two where I found I had pretty much repeated myself. But page by page, the books got written.
You may be shocked that I write in bed (although I'm happy to say my Sunday guests were not shocked at all, and one of them admitted that she often finds herself at 4pm having cleared a good quantity of writing, still in clothes she couldn't possibly leave the house in). But if I need an excuse for writing in bed, please note that Proust did it too. And if it's good enough for Proust it's good enough for me. I don't think it matters where or how you write. I think it only matters that you find out where and how you can write, and do it. Break a few rules. And get going. Really. Just start.