In the 12th Century Japan, the shogunate system began. The head of a shogunate was the shogun. Under the shogun were regional daimyo. Each daimyo had samurai who protected him and his realm. When a samurai displeased his daimyo, as punishment, he would have to endure yubizume, where the first joint of the little finger on the sword hand would be amputated. Although this was a painful punishment, cutting off any finger would have been just as painful, so why did the daimyo choose the little finger?
For major transgressions, the daimyo would simply have the samurai killed, but, for minor transgressions, since the daimyo needed the samurai for protection, he did not want to the punishment to render an unruly samurai incapable of fighting, so he chose to remove the little finger joint. Why did the daimyo choose the little finger?
The other fingers are needed for all types of work and fighting methods, while the little finger seems insignificant. This appears to be a good reason to choose the little finger for amputation, but why was cutting off the little finger more of a disgrace to the samurai than cutting off any other finger?
The reason is that, when holding a sword, the little finger is the finger with the strongest grip. Each finger subsequent finger has a weaker gripping strength than the one before it. Therefore, weakening the little finger's grip would substantially weaken the samurai's grip on his sword, making him a less capable samurai and thus, less a man.
Not only did yubizume serve as a constant and shameful reminder to the samurai, it made the samurai more vulnerable and thus more reliant upon his daimyo. If the samurai further disgraced himself, the next joint of his little finger would be removed. Further transgressions could lead to removal of the joints of the other fingers. Yubizume is still used today by the yakuza (Japanese organized crime families) as a means of punishing their unruly members.
In self-defense situations that require gripping, it is the little finger than has the greatest gripping strength. To demonstrate this, make a tight fist. Then push the index finger of the other hand into the top, thumb side of the fist while noticing how difficult it is to push the finger inside the fist. Now the try the same thing from the bottom, little finger side of the fist. You will notice that it is much more difficult to push the finger into the little finger side of the fist. The little finger has much more gripping strength.
In judo, where you move around a lot while maintaining a constant grip on your opponent, you learn that if you try to grip strongly with all fingers, your hand will cramp, it will stiffer your arm (which will hinder quick movements and telegraph small body movements to the opponent), and your knuckles will rub raw on the rough fabric of the gi. You learn to grip firmly with the little finger while only loosely gripping with the other fingers. When you attack, you may then quickly grip tightly with all the fingers.
When a police officer wants to maintain close contact with a person who, while not unruly at the moment, but may become unruly at any time, he or she may grip the person’s sleeve. If the grip is with all the fingers, the officer’s arm will be stiff and the officer’s body movements will be telegraphed to the person. In addition, the officer will not be able to sense minute movements by the suspect that may indicate an imminent attack. A tight grip with the little finger while the other fingers remain relaxed but ready is not threatening but allows the officer to quickly control the person when needed
When it comes to gripping, the little finger rules.