I only heard this phrase yesterday, but it’s a great image and something that often gets ignored. The red thread is in every single story – it’s what the author wants to happen. Now, you might be justified in thinking ‘yeah, that’s the plot’. But it’s more complicated than that. So long as you can’t see the red thread, everything’s fine and dandy. But what happens when you can?
That needs a bit of explaining. Think of it this way: characters are people too, right? There has to be a reason for them taking the path – telling the story – that they do. Boy meets Girl, Boy falls for Girl, Happy Ever After… but why does Boy fall for Girl? If – as in the example I was reading yesterday – Boy spends the entire time being bossy and disappointed in Girl, and Girl is overawed or downright intimidated by Boy, then why on earth do they end up together? Because the author wants them to. And that’s where the red thread comes into view. These two people spend more and more time in each other’s company, despite clearly not enjoying it, because that’s what the author wants to happen. If the characters were left to their own devices the story would probably be very different, but the red thread is holding them to this specific course.
If the plot falls apart when you take the red thread – the author’s determination – away then you’ve got a problem. Deus ex could be seen as a machination of the red thread – something that wouldn’t happen naturally without the author getting actively involved in pushing the plot forwards. If you as a reader are jarred out of submersion by a strong feeling of ‘that wouldn’t happen’, you’ve just run into a visible red thread. The author’s job is to make this stuff believable (suspension of disbelief notwithstanding), so at no point should their exertion show.
This kind of goes for ‘look how clever I’ve been here’ syndrome as well. Yes, well done, you know a fancy word or found a particularly obscure piece of research. Maybe you spent a long time tracking this down, but if it doesn’t actively contribute to the story in a natural way then does the audience really need to see it? Resist the Urge to Explain, less is more, etc etc.
Basically, as writers we’re all weaving with red thread. Our job is to do it so subtly that no one notices.