Time limitation is not only to protect patent rights, but also to promote the development of science and technology. In a short time, the patentee can't get the benefits he deserves. American President Lincoln said that patent law is to add interest to the fire of genius. However, for a long time, this technology has been in the hands of a few people, and it cannot be widely popularized and applied, which is not conducive to the development of science and technology.
Each country determines the duration of protection according to its own situation.