May I ask why Mo Dou used by carpenters can ward off evil spirits?

Mo Dou, Fang and Bamboo Ruler, the three key tools used by traditional carpenters, are said to have been handed down by Lu Ban's predecessors. They contain the most basic and important contents of the design and construction of clay sculpture carpenters' products. They are called the "masters" of carpenters, representing the ancestors of Lu Ban to some extent, and equivalent to the "sword on the side" of the emperor. Mo Dou is generally made of wood that is not easy to burst, such as camphor wood or ebony, and all the straight lines, saws and saws in the carpenter's work can't be separated from it for almost a moment. There is a story circulating among the Hakkas in Britain and Germany: When Lu Ban first invented Mo Dou, he had to separate the wood from the board or square, and with a slight stroke of Mo Dou line, the wood would be opened quickly and easily. Later, when one of Luban's disciples was working on a project in the mountains, because the ink in Mo Dou's pot was used up and there was no water nearby, the disciple was lazy and didn't want to go far away to get water. He secretly spilled a bubble of urine in Mo Dou's pot, which desecrated the gods and caused the Mo Dou line to unravel. That's when the wood saw was invented. It took a lot of effort to get materials from the saw, and the lazy apprentice was also punished. The old carpenter warned his disciples: be diligent and sincere in everything, and don't be lazy and slippery, otherwise you won't learn skills; When using Mo Dou, Mo Dou dried up. You would rather spit and wet the cotton yarn in Mo Dou than pee in Mo Dou. Mo Dou, Square Ruler and Bamboo Ruler are the embodiment of Luban's predecessors, so the Hakka people in Britain and Germany regard them as gods. Many families also regard them as artifacts to drive away diseases and disasters. When children are shut at home or sick, they will put one of these three tools under the pillow to prevent evil disasters and bless well-being.