The most obvious reason is that if you don't mark it, you can't distinguish the quoted place from the text content. Also, for the rigor of the paper, the format is required, so it must be marked, not marked, and the repetition rate will be calculated together when checking the duplicate, resulting in a very high repetition rate of the paper.

Paper citation description:

Whether it is the proof of academic views, the review of literature review or the theoretical analysis of practical experience evidence, it needs the support of certain literature materials, which will make the written papers more convincing and scientific.

In real academic life, the definition is at the specific level of academic papers, and academic research mainly focuses on two aspects: paper writing and paper publishing, among which paper publishing is more difficult for people to grasp, but the requirements for literature citation are equally high.