Why do Japanese samurai have to carry two knives?

The samurai's sabre is one long and one short. The long sabre is Tai Dao or Dao-beating, and the short sabre is Kodachi. There is a division in the use of the two sabres. The long sabre is the main weapon, and the threat difference is the backup weapon. It is only used when the long sabre is damaged, and it is not usually used. According to the custom, before going out, a samurai will first put a threat in his belt, then hold a knife in his right hand, go to the doorway and put on his shoes, and then put a knife in his belt. The knife is worn on the left waist for the convenience of pulling out the knife with the right hand. Except for short knives, especially the Metezashi short knives for matching armor. In addition, samurai are proud of their swords, and it is considered impolite to bump into the scabbard of samurai (which is why Japanese people walk on the left). Moreover, the sword is worn on the left side, so even if two warriors meet in a narrow alley, their scabbard will not touch each other. When a samurai visits someone's house, he will untie the knife in the porch first, then hold it in his right hand before entering the house. Holding a knife with your left hand into the house means that you can pull it with your right hand at any time, which is a sign of distrust. Unless there is a reasonable reason (being left-handed), it will also be considered impolite.