As students, plagiarizing is a very destructive activity. A student could receive a zero as their grade or even be expelled from their school. So why do students still plagiarize? One theory is that they don't want to do the work on their own. Perhaps they feel like they don't know where to start on an assignment and look at other works for inspiration, but what can start out as inspiration can end up becoming a copy.
How to Avoid It
If you must look at other works for inspiration, or you want to quote another student or author, you have to cite it. If the work is not cited then it is stolen and will be counted as plagiarism. Students need to be careful about what they're writing.