First of all, there may be technical problems in the duplicate checking system. This includes loopholes or errors in the system itself, as well as unstable network connections and other factors. These problems may cause the system to fail to operate normally or have false positives, which will affect the accuracy of duplicate checking results.

Secondly, the judgment of originality is subjective. The duplicate checking system mainly judges whether there is plagiarism by comparing the similarity of texts, but the judgment of similarity is subjective. Different duplicate checking systems may adopt different algorithms and thresholds, resulting in different results. In addition, long-term use of the duplicate checking system may also lead to the distortion of duplicate checking results, because some papers may be submitted and compared many times, resulting in increased similarity.

At the same time, the continuous evolution of plagiarism is also one of the reasons for the failure of duplicate checking. With the continuous progress of technology, plagiarists can use various methods to avoid the detection of duplicate checking system, such as replacing synonyms, changing sentence structure or using metaphors, which makes it difficult for duplicate checking system to identify plagiarism.

Finally, human factors are also an important reason for the failure of duplicate checking. Some authors may modify their papers intentionally or unintentionally to avoid the detection of the duplicate checking system, or they may make a lot of foreign language accomplishments or reorganize the article structure to avoid the detection of the duplicate checking system. In addition, some authors may adopt cooperative writing or ghostwriting mechanism to reduce the detection probability of duplicate checking system.

To sum up, there are many reasons for the failure of duplicate checking, including technical problems, subjectivity of original judgment of papers, continuous evolution of plagiarism means and human factors. In order to improve the accuracy and effectiveness of the duplicate checking system, it is necessary to constantly improve and perfect the system, strengthen user education and publicity, and enhance the author's understanding and attention to academic integrity. In addition, a more comprehensive and detailed evaluation system should be formulated on the basis of duplicate checking system, so as to better identify and punish academic misconduct and promote the healthy development of academic circles.