It's normal. I've only been rejected twice. The reasons for rejection should be carefully read to see if there is room for improvement in the article.

Sending SCI papers is not an easy task, not to mention two rejections. There are many people who refuse to contribute for more than a dozen times, so people have to do what they want.

SCI was rejected for many reasons:

1, high cycle investment. That is to say, you voted for a journal that doesn't match your paper level. A high-level periodical is a good periodical in your eyes, but your paper level may not meet his publishing standards. If you encounter such a problem, then you can throw it away and find a journal with a lower impact factor to continue throwing it away.

The direction of the periodical doesn't match your major.

There is no innovation in the title and direction of your thesis. SCI papers attach great importance to the innovative consciousness of papers. If your paper is trite and not original, or they have published similar papers in their own journals before, then your paper is likely to be rejected.