I can only listen to familiar music, usually without words, when I write.
And I can only write at my best when listening to music.
I know that's strange to some — my wife can't do any kind of thinking work with music in the background — but others know exactly what I mean. My brain is highly associative. People often ask me, "How did you get from this to that thought?" to which the answer is almost always a clear and explainable chain of associations. For that reason, I'm distractable.
I find that music I know "absorbs" and binds wandering tendrils of background thought that might otherwise lead my primary focus off-task.