

Edgar Allen Poe laid out the rules for a fully satisfying revenge in his story The Cask of Amontillado:
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The revenge has to be worse than the original offense.
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You have to get away with it.
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The person has to know who did it, and why, yet there’s nothing they can do about it.
Take away any of those factors, and it isn’t a fully satisfying revenge plot.
Yeah, the interest idea doesn’t make sense, especially since for most of the 21st century the interest on savings accounts has been negligible.
If it cost $6 on the $1500 loan, that’s most (of not all) of the interest right there, and it takes time for that interest to accrue significantly. It’s not going to happen in a couple of days.
If this was the scheme, then your ex-boss was no criminal mastermind.