What Is a Beat Sheet
A beat sheet is a list of the major turns in a whole book, named and placed at roughly the points where they tend to land: the event that starts things moving, the point where the situation gets worse, the moment right before everything seems lost. The best-known version comes from screenwriter Blake Snyder's Save the Cat! (2005), which named fifteen such turns for film and got adopted widely by novelists looking for a shared vocabulary. It's the most usable of the major structure tools, and, for the same reason, the easiest one to lean on too hard.
Where the confusion comes from
A beat sheet gets sold, often, as a recipe: hit these turns at these percentages and the story will work. That oversells what it actually is. A beat sheet describes a pattern that shows up often in stories that work, not a set of ingredients that guarantees one will. Two novels can hit the exact same beats in the exact same order and land completely differently, because the beats only describe when something happens, never why it matters to the specific people the book is actually about.
How this shows up in a real novel
Frankenstein (Mary Shelley, 1818) has a beat sheet that reads clearly in hindsight: Victor creates his creature, abandons it in horror, the creature kills Victor's younger brother, the creature demands a companion, Victor destroys the unfinished companion, the creature kills Victor's bride on their wedding night, and Victor chases his creation north until the pursuit consumes him. Naming those turns says nothing about the novel's real engine, which is the gap between what Victor expects his ambition to cost him and what it actually costs.
While you're drafting
A beat sheet is most useful as a diagnostic after a draft exists, a way to check whether the major turns are actually there, rather than as a template to fill in before a single scene gets written.
Questions
Is a beat sheet the same as an outline? No. An outline can include everything that happens. A beat sheet is narrower: only the handful of turns that shift the whole story's direction, named and roughly placed.
Does every good novel follow the same beat sheet? Not exactly the same one, and not on purpose. The pattern shows up often enough to be worth knowing, but plenty of well-built novels land their major turns at different points, or skip one entirely.
Should a beat sheet be written before drafting starts? It can be, but it works just as well built afterward, as a way to check a finished draft for the turns it might be missing rather than a set of boxes to fill in advance.