-Short replies don’t help — you need to write like you're helping someone.
What is helpful is helpful and its length as short or long is not matter.
Who told you that short replies are not helpful?
When trying to write quality posts, a lot of people act as though they're writing a book report for school: putting facts that we already know into their own words. Nobody wants to read that, and you will not get merit for it. Moreover, the length of your post and the quality of your English are only minor factors. In trying to write a quality post worthy of merit, you should offer new ideas, personal experiences, or perspectives that other forum users will actually find new and interesting.
-Original thinking matters — don’t copy anything, not even from your own posts.
You don't always have original thinking but if you use content from somewhere else, you must inform other forum members with source links. If you ignore source links, you plagiarize and your account will be banned.
Plagiarism: If you copy some text from somewhere, then you should have a good reason for it, and you must link to the source. Doing otherwise is plagiarism. Changing a few words around doesn't matter. If we find that you plagiarized, then you absolutely will be permanently banned, even if we find it years after you did it.
33. Posting plagiarized content is not allowed.[e]