The notion basically is that if i were able to keep everything else in the universe fixed, but change one fact, does that have effects down stream. If you could imagine putting a person there raising their umbrella, would it start raining? No. If you imagine it raining and that someone who didn't have their umbrella up, would they raise their umbrella? Yes. So that's the direction in which the causality goes. And that's a story you can forward in time, because entropy is increasing. It's not a stories you can tell backward in time.