1. Mathematical perspective, cost saving. When the circumference is fixed, the circle area is the largest, and the near circle can save raw materials. This is also the first reason to promote the circle.
2. Aesthetic angle, lasting ugly. The long-term habit of forming a circle is more in line with the aesthetic.
3. The manufacturing angle and process are simple. Whether it's glass or plastic, it's easy to make a circle. Other shapes need to be remade, and the process is difficult to guarantee.
4. Behavioral perspective, convenient to use. The round shape is consistent with the result of human body, which is convenient for grip strength.