There has always been a bias toward people who work better with their left hand. Ever since it became established that the herald of the devil was left-handed. Another factor (for many) is the fact that the Devil lives in the left half part of the body.
Even in most modern languages, "left-handed" means insincerity, betrayal, dishonesty.
Statistically speaking, 7 out of 100 people are born left-handed. Many of them, as children, were encouraged to write with their right hand. An old superstition goes that if you force a left-handed child to write with his right hand, they will turn into a stutterer. However, a small part of these people learn how to write with both hands - an ability that impresses others. But nothing more.
Generally, left-handers are expected to be clumsy. In the Book of Judges from the Old Testament, it is said: "Among all these were 700 chosen men who were left-handed; every one could sling a stone at a hair and not miss."
One of the most famous people that worked with their left hand was Leonardo da Vinci. He painted the Mona Lisa with his left hand.
When it comes to the subject of left-handers, Muslims are especially sensitive. Muslim belief states that each person has 2 guardian angels. The one standing on a person's right side records all the good deeds. The one standing on the left - the bad deeds. And that is not all.
It is said that after Creation, Allah tossed a handful of dirt on his right side and thus created humans, that were predetermined to have luck. Then he did the same on the left - and thus made the unlucky. For these reasons, Muslims use their left hand for all activities that they believe to be unclean, such as petting a dog.
During the Middle Ages, to be left-handed was one of the countless reasons by which you could be accused of using sorcery. And therefore, be burned at the stake.
There are many beliefs related to the left side in general. For example, if you get up from bed on its left side. It is considered such a bad omen, that some hotel rooms are furnished in such a way that you cannot get up from the left side.