According to Weidenborner and Caruso, authors of Writing Research Papers: A Guide to the Process, plagiarism is a serious offense and is considered so by instructors/professors, as well as by readers and writers in general.
Generally speaking, when reading your essays or research papers, instructors want to know what information is coming from someone else, and what information is coming from your own original thoughts and judgments. Having proper citations shows your instructor that you are trustworthy and have personal integrity (145).
Weidenborner, Stephen, and Domenick Caruso. Writing Research Papers: A Guide to the Process. Boston: Bedford/St. Martins, 2001. Print.
According to Rozakis in The Complete Idiot's Guide to Research Methods, you are plagiarizing if...
Rozakis, Laurie, Ph.D. The Complete Idiot's Guide to Research Methods. New York: Alpha Books, 2004. Print.