Retention curve
The graph of how many viewers are still watching at each moment of a video.
A retention curve plots the proportion of viewers still present against time. It's the diagnostic version of watch-through: instead of one summary number, you see exactly where people left.
Read it for shape, not level. Nearly every curve drops steeply in the first few seconds. That's people deciding whether this is for them, and it's normal. What's diagnostic is what happens after: a smooth gentle decline means the piece is holding, a sudden cliff means something specific went wrong at that timestamp, and a rise means people rewound or a section pulled them back in.
The cliffs are the gift. Note the timecode, open the edit, and watch the ten seconds before it. The answer is almost always visible: a slow section, an unearned tangent, a graphic that took too long to pay off.
Where this comes up
A hook isn't a slogan. It's the first structural move of a piece, and it makes a promise the rest has to keep. The five that work and why.
By the final cut you've lost the ability to see it. A structured last pass that catches the things familiarity hides, in about forty minutes.