How many people actually take a secret to the grave?

Ideally, everything comes to light and lies are discovered. That's always the happy ending.

However are there times someone literally dies without revealing their secret (can be anything ranging from minor to major ones such as the cheater or the partner dying, never finding out they got cheated on for years), how many people have done that and still do that?

Out of those happy ending where the truth is discovered, how many real life stories have sad ending where the liar literally got away with it and died with the secret?

How many people actually take a secret to the grave?
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