The first category: the quality of the paper is too poor to pass.
This kind of paper is usually patchwork, without its own core value and conclusion, and is common in master's thesis. Many graduate students don't study for scientific research, but want to improve their academic qualifications and find a good job, because they didn't put their time and energy into scientific research during their study.
Graduation is near, and I am ready to send it out for blind graduation with a slight modification on the data of seniors and even younger siblings. In order to get rid of such people, the boss generally does not restrict sending them to trial work. This kind of paper lacks its own logic, and even the basic paper format is not necessarily correct. Even if the relationship between experts and bosses is no matter how good, there is still a basic bottom line for scientific research. It's not surprising that it was filmed by blind experts.
There are not a few such papers. Even in the relatively good 985 schools, there are a large number of examples that fail to pass the blind evaluation because of the shoddy papers every year.
The second category: blind experts can't understand, and the author of the paper is unlucky.
Not all blind experts can understand the content of the paper. With the development of modern science, neighbourhoods have been subdivided very complicated, and sometimes small differences will lead to experts in different fields not knowing each other. Therefore, some papers were killed because the authors and tutors did very little and it was difficult to send them to experts in the same field. It can only be sent to experts who seem to be close in the general direction, but actually don't understand at all.
Generally, experts will be very careful when they encounter papers they don't understand, but some experts would rather kill 3 thousand papers they don't understand by mistake than let go of one. You can only blame yourself for your bad luck when you meet such a blind expert.
The third category: the paper has a certain subjective "hard injury"
For this kind of paper, even if the content of the paper is logically complete and the theory is correct, it may be strangled because the blind reviewer does not recognize part of your content. The most typical example is the debate in physics about the wave-particle duality of light. Scholars of the two schools do not recognize each other and are incompatible with each other. There are countless similar examples. If what you do happens to be controversial in academic circles, you can only ask for your own blessings and see if you can send it to "hostile" experts.
Another situation also comes from the subjective judgment of experts. Based on his own experience, he may think that what you have done is not innovative, or there is some plagiarism, or what you have done is worthless, that is, the paper may have some subjective "hard injuries" or it may not be given to you. These are all based on the subjective judgment of the judging experts themselves, and it may be a world of difference for another expert to evaluate them.