Flashback

A flashback is a scene set earlier than the story's present, dropped into the forward narrative to dramatise something that has already happened.

Sol Stein's On Writing passes on the shortest advice anyone has given on the subject: asked how best to handle flashbacks, the master's reply was Don't. Ideally, all fiction seems to be happening now.

That is a starting position rather than a ban, and the exceptions are specific. A flashback earns its place when it illuminates the present story in a way nothing in the present could — when the reader learns something there that changes what the current scene means. Flashbacks used purely for character backstory stall the book instead, because backstory is information and the reader wanted a scene.

Two practical handles. In prose, keep short memories inside interiority and write them in fragments, since that is how recall actually arrives — flashes of image rather than continuous footage — and trigger them through a sense, the way memory is triggered in life. In a screenplay, mark the exit explicitly: END FLASHBACK, or RETURN TO PRESENT in the slugline, every single time. The only thing worse than an unnecessary flashback is a reader who cannot tell they have left it.

And make the first sentence of a flashback arresting. It is a second opening, and it competes with the story it interrupted.