Things That Exist Can Be Explained

Everything has an origin. Nothing magically appears or occurs without reason. As the author, you need to be able to explain the things that happen in your stories. They need to be plausible and realistic.

This gives you a stronger connection with your audience. They trust you when they know everything has a reason. Without that trust, they cannot invest in what you have to say, and your credibility is everything.

When authors have actions that make no sense, or characters who start acting noticeably wrong, that is a deus ex machina. It's a cheap plot device to save a story when you set stuck in an inescapable situation.

Things that exist can be explained. This includes people, clothing, drinks, music, and almost anything you'd say. Know enough to be able to explain them, and use that knowledge to inspire you to come up with more interesting stories use these explanations and don't pull out deus ex machinas on  your audience.