This article by David Byrne, initially about collaboration, is one of the best things I’ve read about the whole joy/pain of songwriting in general.
As for collaboration, I’ve often noticed that I feel far more creative when I’ve arranged someone else’s song – Lynsey Hutchinson, Fiona Thom – than when I’m doing my own. And on the rare occasions when I’ve handed something over to a collaborator to arrange – The Desert Was Better (Dave Watson), Hungry Ghosts (Iain McKinna) – I’ve resisted the results at first then accepted them as better than I would have done. The only true collaboration I’ve done on a song was when Nelson, Lindsay, Fiona, Karen and I made up a track during a day in Arran, and I was despatched to the dining room table to come up with some words and a tune. I loved it. (The result is here.) Maybe I should get out more!