Here’s an interesting article on how Handcuffs came into existence.

The Sordid History and Evolution of Handcuff Design

Handcuffs have unusual and contradictory design requirements: They must serve one human, and at the same time thwart another.
For those who wield handcuffs, they must be light and efficient to put on and remove from a perpetrator. For the unfortunate wearer, the devices must restrain resistant wrists whether they happen to be thick or thin. And cuffs can’t succumb to cleverness or brute force escape attempts.