Sato's probably counting on the interest accruing if the payment is even ten minutes late. Typical loan shark behavior, get them when they're in a compromised position, and offer terms that seem like they might be handable... but turn out to not be after all, and you're suddenly and effectively someone else's financial slave, doing more and more unspeakable things in an effort to actually get out from under the debt.
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"You know how parents tell you everything's going to fine, but you know they're lying to make you feel better? Everything's going to be fine." - The Doctor
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"You know how parents tell you everything's going to fine, but you know they're lying to make you feel better? Everything's going to be fine." - The Doctor