The Cold Open vs. The Prologue
A cold open drops the reader mid-action without context or orientation — an event in progress, a question without an answer, a voice without a name. A prologue provides context: backstory, history, a death before the main story begins, a perspective that frames what follows. Both must justify their existence or they will be skipped — and readers who skip prologues are a significant portion of your audience. The test for both is the same: does the main story make less sense without it? If you can delete the pre-chapter material and the novel still works, it was probably not necessary.